Walkthrough metal detectors have become a common sight in public buildings, entertainment venues and high-security areas. They provide a quick way of checking people for concealed metallic objects without requiring every visitor to undergo an immediate physical search. Also known as archway metal detectors, security arches or knife arches, these devices are commonly used to detect guns, knives, tools and other metal objects carried on the body. However, buying a walkthrough metal detector is not simply a matter of choosing the model with the largest number of detection zones. The arch must suit the threat being searched for, the location in which it will operate and the number of people expected to pass through the checkpoint.
To find out about specific models, you can also check out our guide on the best walk through metal detectors in the UK.
Understanding Walkthrough Metal Detectors
Walkthrough metal detectors are security devices used to detect metallic objects on people passing through them.
The term “knife arch” is widely used in the UK, particularly when the detector is being used as part of a knife-screening operation. It can be slightly misleading, though, because the detector does not identify an object as a knife. It detects the presence of metal and produces an alarm when that metal meets the detector’s programmed threshold.
It is then the operator’s job to establish what caused the alarm.
A detector may respond to a weapon, but it may also respond to a phone, keys, steel-toe-capped footwear, a belt buckle or several smaller items carried close together. This is why a clear search profile and a proper alarm-resolution procedure are just as important as the equipment itself.
Walkthrough metal detectors also have limitations. They are designed to detect metal and should not be relied upon to find ceramic knives, plastic weapons, explosives or other non-metallic prohibited items. Where those threats form part of the risk assessment, the arch will need to be used alongside other search methods.
How Do Walkthrough Metal Detectors Work?
Walkthrough metal detectors operate using electromagnetic fields.
When the detector is switched on, its panels create a controlled electromagnetic field inside the passageway. A metallic object passing through this field causes a measurable disturbance. The detector analyses that disturbance and sounds an alarm when it exceeds the selected threshold.
Modern detectors can do more than provide a simple yes-or-no alarm. Multi-zone models indicate the approximate position of the metal on the person’s body, usually by illuminating LEDs on the side panels or showing a location on a display.
This helps the operator decide where to concentrate a secondary search. An alarm around the lower-left leg, for example, can be checked more quickly than carrying out an unfocused search of the whole body.
The detector cannot tell the operator with certainty what the object is. Even the most expensive model still requires trained staff and a sensible procedure behind it.
Begin With the Search Profile
Before choosing a detector, the organisation should decide what it is actually trying to find.
This is known as the search profile.
A venue mainly concerned about large knives and firearms may want to disregard ordinary pocket items where possible. A prison, examination centre or manufacturing site may need to detect much smaller pieces of metal, including improvised blades, electronic devices or components being removed from the premises.
Higher sensitivity is not automatically better. Turning the detector up too far may cause repeated alarms from harmless personal belongings. That slows the queue, frustrates visitors and places more pressure on search staff.
A useful search profile should set out:
- The objects that must be detected
- The harmless items that can reasonably be ignored
- Whether visitors will empty their pockets before screening
- What happens after an alarm
- The maximum acceptable queue and delay
- Whether different groups require different screening arrangements
The equipment should then be tested against representative objects rather than being left on whichever factory setting happens to be selected.
Not All Walkthrough Metal Detectors Are Equal
Although walkthrough detectors work on broadly similar principles, there are substantial differences in their construction, controls, detection systems and intended use.
The right model is the one that fits the operation. A feature that is valuable at an airport may add little at a school or temporary event.
Sensitivity Levels
Most professional walkthrough metal detectors provide adjustable sensitivity settings. These allow authorised staff to alter the amount of metal needed to trigger an alarm.
Some models also allow different parts of the detector to be adjusted separately. This can be useful where harmless items regularly cause alarms in one area of the body.
The RISK P1 Portable Knife Arch, for example, has 24 detection areas and allows sensitivity to be adjusted by area. An operator could reduce sensitivity around the upper body to limit alarms from jewellery while retaining greater sensitivity around footwear or trouser pockets. It also offers up to 255 sensitivity levels.
The Garrett PD6500i offers up to 200 sensitivity levels, more than 20 application programmes and adjustable sensitivity boosts across selected parts of its 33-zone detection area.
The numbers are useful when comparing control options, but they do not tell the whole story. Stability, calibration, interference rejection and the quality of the operator’s testing all affect real-world performance.
Multi-Zone Detection
Detection zones divide the passageway into sections so the operator can see the approximate location of the metal.
Older detectors may have only a few broad zones. More recent models can divide the body vertically and horizontally, with indicators showing whether the alarm came from the left, centre or right.
The RISK W2 has 18 detection areas, while the RISK TD1 and Garrett PD6500i each have 33. The Garrett Paragon has 66 zones, arranged across the left, centre and right of 22 horizontal bands.
More zones can make secondary searching quicker, particularly when a person is carrying metal in more than one location. They should not, however, be confused with greater basic detection sensitivity.
A properly configured 18-zone detector may be more useful than a 66-zone detector installed in a poor location or operated by staff who have not been trained.
Fixed, Semi-Portable or Fully Portable
Walkthrough metal detectors are often described as portable when they are merely capable of being moved.
There is an important difference between a detector with wheels and one designed to be regularly dismantled, transported and reassembled.
The RISK W2 is semi-portable. It has wheels and can be tilted for movement over short distances, but it is a mains-powered indoor detector weighing around 45kg. It is best suited to a building where it may occasionally be moved between entrances.
The RISK P1 is a fully portable model. Its components stack together for transport, and trained staff can assemble it in approximately five to seven minutes. It can operate from the mains or from its internal battery for up to nine hours.
The Garrett PD6500i and Garrett Paragon are better suited to fixed or semi-permanent checkpoints. They can be dismantled and relocated, but their weight and construction do not lend themselves to being transported between events every week.
When portability matters, buyers should ask to see the full transport process. A demonstration in which a supplier merely wheels an assembled detector across a smooth showroom floor does not prove that it will be convenient to load into a vehicle and deploy at a muddy event site.
Indoor and Outdoor Use
Not every walkthrough metal detector can be left outside.
An IP rating gives an indication of resistance to dust and water, but the full specification should be checked. Cables, plugs, control panels and power supplies must all be suitable for the intended location.
The standard RISK P1 is rated IP54 and is supplied with a separate rain cover. This makes it useful for temporary outdoor checkpoints where the weather may change during an event. It should still be deployed carefully, with the cover fitted correctly and the power arrangements protected.
The RISK TDX is intended for permanent outdoor operation. It has an IP65 rating, weather-resistant construction, a waterproof display and 33 detection zones. It can also be secured to the ground, making it more stable than a lightweight portable arch.
Garrett offers weather-resistant fixed detectors as well. The standard Garrett PD6500i is available in IP55 and IP65 versions, while the Garrett Paragon is listed as IP65.
An outdoor rating does not mean the detector can be placed anywhere without thought. The checkpoint still needs a level surface, safe electrical supply, suitable lighting and protection from vehicle movements, crowd pressure and deliberate interference.
Power and Battery Operation
Fixed detectors normally run from mains electricity. Batteries may be provided for emergency backup rather than everyday operation.
The Garrett Multi Zone includes an internal battery providing approximately one hour of backup power, with a larger optional battery available for longer operation. The Garrett Paragon has a similar arrangement, with an integrated short-term backup and an optional extended battery.
The RISK P1 is intended to operate from its battery as part of normal portable use. Its 12,000 mAh battery can provide up to nine hours of operation, depending on conditions and settings.
Battery figures should be treated as maximums rather than guarantees. Age, temperature, alarm frequency and charging history can all affect running time. For a full-day event, a charging plan or alternative power source is sensible even when the quoted battery life appears sufficient.
Operating Frequencies and Interference
Metal detectors can be affected by nearby electrical equipment, structural metal, reinforced flooring and other walkthrough detectors.
A detector that works correctly in a warehouse demonstration may behave differently when installed beside automatic doors, barriers, radios, power cables or another security arch.
Models such as the RISK TD1 provide a choice of operating frequencies so several units can be configured to work near each other. The Garrett Multi Zone includes an automatic scanning function that checks the electromagnetic environment and selects a suitable frequency.
This does not remove the need for a site survey and operational testing. The final settings should be established where the detector will actually be used.
The Department for Transport notes that two examples of the same detector may require different settings because of the environmental conditions at their installation sites.
Displays, Counters and Remote Management
Current detectors may include colour displays, directional counters, alarm counters, password-protected settings and network connections.
These features can be useful, but only when the organisation has a plan for using them.
A built-in counter can help estimate throughput or occupancy. Password protection prevents unauthorised staff from changing security settings. Network management may help a large site check several detectors from a central location.
The Garrett Paragon adds Ambiscan, which allows different detection settings to be used according to the direction of travel. A workplace could therefore search people entering for weapons while using a different setting to detect company property being taken out.
For a small venue operating a single entrance, that facility may not justify the added cost. Buyers should separate features they will genuinely use from features that merely look impressive on a specification sheet.
Choosing Between RISK and Garrett Models
RISK and Garrett cover several different parts of the walkthrough-detector market.
RISK models tend to provide a large number of adjustable features at comparatively accessible prices. They are particularly worth considering where portability, outdoor operation or purchase cost is the main concern.
Examples include:
- RISK W2: A lower-cost, 18-zone indoor detector for fixed or occasionally moved checkpoints.
- RISK TD1: A 33-zone fixed detector with a touchscreen, targeted alarm display and individually adjustable zones.
- RISK P1: A 24-zone modular detector intended for regular transport and temporary deployment.
- RISK TDX: A 33-zone IP65 detector intended for permanent outdoor use.
Garrett has a long-established position in aviation, government, event and correctional security. Its models generally cost more but are well suited to organisations that place particular weight on established product history, construction and international testing.
Examples include:
- Garrett Multi Zone: A 20-zone detector with automatic frequency selection, battery backup and a straightforward control system.
- Garrett PD6500i: A widely used 33-zone detector with numerous security programmes, adjustable sensitivity and optional network management.
- Garrett Paragon: A 66-zone detector with Ambiscan, mobile-phone discrimination, NFC access and an IP65 rating.
Neither brand is automatically right for every site. A portable RISK P1 may be the better choice for an events company, while a Garrett PD6500i or Paragon may make more sense at a permanently staffed high-security entrance.
The decision should come back to the search profile, operating environment and available staff.
Where Are Walkthrough Metal Detectors Commonly Used?
Walkthrough metal detectors are used in locations where there is a need to prevent weapons, unauthorised electronics, tools or other metallic objects from being carried into or out of a controlled area.
Common locations include:
- Airports and transport sites
- Government and public-sector buildings
- Courts and correctional facilities
- Schools, colleges and universities
- Stadiums, arenas and exhibition centres
- Nightclubs and licensed entertainment venues
- Factories, warehouses and data centres
- Public events and temporary security operations
The screening arrangement should be proportionate to the risk. A poorly planned checkpoint can create long queues, block escape routes and move crowds into an exposed area outside the venue.
NPSA guidance recommends treating the screening of people and their belongings as part of the wider security plan rather than as a stand-alone piece of equipment. At high-footfall locations, the balance between threat detection, delay, space and staffing becomes particularly important.
Standards and Legal Requirements
There is no single UK law requiring most venues to install a walkthrough metal detector.
The need for screening will usually come from the organisation’s risk assessment, operating licence, contractual requirements, regulator or sector-specific security directions.
The former Centre for the Protection of National Infrastructure, usually known as CPNI, is now the National Protective Security Authority. NPSA is the UK Government’s National Technical Authority for physical and personnel protective security and publishes guidance on search and screening.
Manufacturers may also state that their equipment conforms to standards such as NIJ Standard 0601.02 or various aviation requirements. These claims can help when comparing products, but they should not replace a site-specific test and documented operating procedure.
Aviation
Aviation security operates under its own requirements.
The Department for Transport no longer certifies or provides the initial installation settings for walkthrough metal detectors. For aviation use, initial settings should be established at installation by the manufacturer, and the operator must carry out the required daily and weekly tests. Settings may need to differ between sites because of local environmental conditions.
An organisation should not assume that a detector described as “airport grade” is automatically approved for any aviation-security task.
SIA Licensing
The use of a walkthrough metal detector does not create a separate category of SIA licence.
However, staff carrying out licensable security work may need the appropriate front-line licence. Contract security guarding is normally licensable, and door supervision at licensed premises requires a door-supervisor licence, including for in-house staff. Some exemptions apply, including particular aviation-security roles and some in-house arrangements.
Organisations should check the duties being performed rather than relying on the employee’s job title.
Equality, Accessibility and Alternative Screening
The screening process must be applied fairly and should account for disability, religion, medical devices and other individual circumstances.
The Equality Act 2010 protects people from discrimination in employment, services and wider society. Public bodies also have additional equality duties when designing and delivering services.
Not everyone will be able to walk through a standard arch. The checkpoint should therefore include an accessible alternative, with trained staff able to explain what will happen.
People with medical implants may also request or require an alternative search method. Government airport guidance, for example, says that a person with an implantable cardioverter defibrillator can ask for a hand search and that a hand-held detector should not be placed over the device. Manufacturer and medical advice should always be followed.
Planning the Checkpoint
The detector is only one part of the checkpoint.
Space is also needed for signs, queue barriers, divesting tables, trays, secondary searches and the return of personal belongings. A private search area may be required depending on the site and the type of searches being conducted.
Before installation, consider:
- Where people will queue
- Which items they must remove
- Where removed items will be placed
- How alarms will be resolved
- How people will rejoin the main flow
- What happens when someone refuses screening
- How an accessible alternative will operate
- How staff will summon assistance
- How the checkpoint affects emergency evacuation
A common mistake is to concentrate on the detector’s advertised throughput. An arch may reset in less than a second, but the real screening rate is usually determined by how quickly people empty their pockets and how efficiently staff deal with alarms.
Standard Procedures for Walkthrough Metal Detector Use
To maintain an orderly and effective screening point, the organisation should have a written procedure covering normal operation, alarms, refusals, prohibited items and equipment faults.
1. Test the Detector Before Use
The detector should be switched on, allowed to complete its startup checks and tested using an agreed test object.
The test should confirm that the object is detected in the required positions, including around the upper body, waist, legs and footwear. The result should be recorded where the site’s procedure requires it.
Checks should be repeated after the detector has been moved, after settings have changed or when interference is suspected.
2. Prepare the Screening Area
The detector should be positioned so that people cannot easily walk around it.
Nearby metal structures and electrical equipment should be considered, and the route through the arch should be kept clear. Tables and crowd-control barriers should not be placed so close that they affect operation or obstruct staff.
3. Give Clear Instructions
Visitors should be told what to remove before approaching the arch. At a typical venue this may include phones, keys, coins and other large metal items.
Instructions should be visible and consistent. Repeatedly changing the rules from one person to the next causes confusion and makes the checkpoint appear arbitrary.
4. Screen One Person at a Time
People should pass through at a normal walking pace without touching the side panels.
The next person should not enter until the detector has reset. Bags and loose belongings should not be carried through unless that forms part of a specifically tested procedure.
5. Resolve Every Alarm
An alarm should never be ignored simply because the queue is becoming long.
The person may be asked to check their pockets and pass through again. If the alarm continues, staff can use a hand-held metal detector or conduct a physical search in accordance with the site procedure.
Multi-zone indicators should guide the search, but staff should not assume that the illuminated area is exact to the centimetre.
6. Deal With Prohibited Items
The procedure should state what staff must do when they find a prohibited item.
The correct response will depend on the object, the venue’s conditions of entry, the person’s behaviour and whether there is an immediate danger. Staff should know when to refuse entry, call a supervisor, isolate an area or contact the police.
7. Record Faults and Significant Incidents
Equipment faults, repeated unexplained alarms and changes to settings should be logged.
Serious incidents should be recorded under the organisation’s reporting procedure. The detector’s traffic counter may provide useful operational information, but it should not be treated as a substitute for an incident report.
Staff Training
A walkthrough metal detector should not be handed to staff with the instruction to “turn it on and watch for the red light”.
Operators need to understand:
- What the site is searching for
- Which programme and sensitivity setting should be used
- How to test the detector
- How to recognise possible interference
- How to direct people through the arch
- How to interpret zone indicators
- How to use a hand-held detector
- How to carry out or arrange a lawful secondary search
- How to respond to refusals and prohibited items
- How to assist disabled people and those with medical devices
Supervisors should also know who is authorised to alter settings. Passwords and control keys should not be left where any member of staff can change the detector without recording it.
Maintenance and Storage
Walkthrough metal detectors have relatively few moving parts, but they still need basic care.
Panels, cables, connectors and control units should be checked for damage. Portable models should be packed in the correct order, and batteries should be charged and inspected according to the manufacturer’s instructions.
Outdoor covers must be allowed to dry before long-term storage. A wet cover packed tightly around the detector can cause damage even when the arch itself is weather resistant.
A detector that is dropped, struck by a vehicle, exposed to water beyond its rating or transported without protection should be checked before it returns to service.
Common Buying Mistakes
The most common mistake is buying from the specification sheet alone.
A large number of zones, an impressive screen and hundreds of sensitivity settings do not guarantee that a detector will work well at a particular site.
Other mistakes include:
- Buying an indoor detector for an uncovered entrance
- Treating a wheeled detector as a genuinely portable model
- Forgetting the cost of batteries, covers, test pieces and hand-held detectors
- Installing the arch without checking for interference
- Setting sensitivity too high and creating constant alarms
- Having no procedure for people who cannot use the arch
- Failing to provide enough staff for secondary searches
- Allowing unauthorised staff to change settings
- Assuming the arch can detect non-metallic threats
Where possible, the buyer should arrange a demonstration using realistic test objects and, ideally, test the proposed model at the intended site.
Final Thoughts
Walkthrough metal detectors can make security screening faster and more consistent, but they are not a complete security solution on their own.
The model must be chosen around the search profile, location and operating pattern. A RISK P1 may suit a security company moving between events, a RISK TDX may suit an exposed outdoor entrance, and a Garrett PD6500i or Paragon may be more appropriate for a permanent high-security checkpoint.
Whichever model is selected, its performance will depend on sensible settings, regular testing and operators who know what to do when it alarms.
A well-run 18-zone detector is more useful than a badly run 66-zone detector. The equipment matters, but the procedure around it matters just as much.
Walkthrough metal detectors have become a common sight in numerous public spaces and high-security areas, playing a vital role in ensuring safety by detecting concealed metallic objects. This article delves into the intricacies of walkthrough metal detectors, exploring their functionality, applications, and the standard procedures associated with their use.