From a couple of metres for a passive tag on a compact reader to well over ten for an active tag with a large antenna - and the installed figure is always less than the specification.

Passive tags draw their power from the reader's field, which limits the range and makes it dependent on antenna size and transmit power.

Active tags transmit using their own battery and reach much further, at a higher unit cost and with a battery to replace.

Real range is reduced by weather, by the angle of approach, by the vehicle's body and glass, and by anything metallic near the antenna.

More range is not automatically better. An over-ranged reader opens the gate for vehicles that were not coming in.

Size the range to the lane: enough that the barrier is moving as the vehicle arrives, not so much that it triggers from the road outside.

By shaping and restricting the read zone - directional antennas, careful aiming, power reduction, and a loop or sensor that confirms a vehicle is actually in the lane.

The classic failure is a reader that opens the gate for a tagged vehicle sitting in the exit lane or queuing on the road.

Directional antennas concentrate the field along the lane instead of spraying it around, and are the first tool.

Reducing transmit power tightens the zone, and is usually adjusted on site rather than calculated in advance.

An inductive loop or presence detector in the lane provides the definitive check: no vehicle present, no barrier movement, regardless of what was read.

Commission by driving the actual approach, including the adjacent lanes, rather than by walking a tag around.

Passive where the required distance is modest and there are many vehicles; active where the distance is genuinely long or the traffic is fast.

Passive tags are inexpensive, have no battery, last indefinitely and can be issued freely - typically as a windscreen sticker that is destroyed on removal.

Active tags read much further and more reliably at speed, and are usually a dashboard or windscreen unit.

The active battery has a finite life, so the estate needs a replacement programme and the reader should report low battery before failure.

Cost per vehicle differs enough that a large fleet may be affordable with passive tags and not with active ones.

Mixed deployments are common: passive for staff parking, active for a fast commercial lane or a barrier that must open early.

No. It identifies the vehicle, and that distinction is the most important thing to design around.

Whoever is in possession of the vehicle - or of a sticker peeled from it - passes the barrier, and the audit trail names the tag holder.

Where personal identity matters, pair the vehicle credential with a driver credential presented at the same point, or with an intercom and camera.

Number plate recognition can cross-check that the tag and the plate belong together, which detects a transferred tag.

Tamper-evident tags that destroy themselves on removal make transfer harder, and are worth specifying for that reason alone.

Write the policy down: what a vehicle tag entitles someone to, and which areas require a person to be identified as well.

They can block it completely - metallised coatings and heating elements form a screen that many tag technologies cannot get through.

Vehicles with these windscreens usually have a small uncoated aperture, often behind the mirror, intended for toll transponders and similar devices.

The tag must be placed inside that aperture. Fitted elsewhere on the glass it will read erratically or not at all.

Where no aperture exists, alternatives are a headlamp-area tag, a tag fitted externally, or a different technology such as plate recognition.

This is a frequent source of intermittent faults on mixed fleets, because it affects some vehicles and not others and looks like a reader problem.

Include the check in the tag fitting instructions and train whoever issues them.

Long-range readers use nationally allocated bands with limits on frequency and power, so equipment approved in one territory is not automatically legal in another.

The ultra-high-frequency bands used for these systems differ between regions, and so do the permitted transmit powers and duty cycles.

A reader imported from another market may transmit outside the local allocation, which is an offence and can interfere with licensed services.

Tags are matched to the reader's band, so a mismatch simply does not work - which at least fails visibly.

Buy equipment approved for the country of installation and keep the declaration with the project documentation.

For multinational estates, expect to specify regional variants rather than one part number, and check before shipping spares across borders.

High enough and angled so the field covers the windscreen at the stopping point, clear of metal, and robust enough for weather, vibration and impact.

Mounting height and downward angle determine whether a windscreen tag is inside the read zone. Get it wrong and tall vehicles read while cars do not, or the reverse.

Metal barriers, posts and gates near the antenna distort the field. Manufacturers publish clearance requirements and they should be respected.

Weather protection, ultraviolet stability and a wide temperature range are all baseline for an external installation.

Vibration is real on a barrier post. Mount to a rigid structure rather than to the moving equipment.

Cable runs to a gatehouse are often long, so check the maximum distance for the reader interface and plan the containment and surge protection with the civils rather than afterwards.