Why start from your crashes?
Camera alarms are not all equal for every fleet. A tanker fleet that runs at night needs a different set from a city bus fleet. Choosing alarms from your own crash and near-miss history keeps drivers from hearing alarms that do not match their risks, and keeps the review team focused.
Which alarm addresses which crash?
| Crash or near-miss type | Main alarm | Also helps |
|---|---|---|
| Rear-end crashes | Forward collision warning, Headway monitoring | Distraction alert, Phone use alert, Fatigue alert |
| Close following | Headway monitoring | Forward collision warning |
| Lane drift and run-off-road | Lane departure warning, Fatigue alert | Distraction alert, Phone use alert |
| Pedestrians and cyclists | Pedestrian collision warning | Blind-spot detection, Distraction alert |
| Side and turning collisions | Blind-spot detection | Lane departure warning |
| Drowsy driving | Fatigue alert | Lane departure warning |
| Phone use | Phone use alert | Distraction alert |
| Looking away | Distraction alert | Phone use alert |
| Smoking in the cab | Smoking alert | None |
| No seatbelt | Seatbelt alert | None |
| Covered cameras | Camera cover alert | None |
This mapping was written for this page from how each alarm works. It is not taken from a standard. Adjust it to your own review findings.
Where do the cameras go?
| Camera | Position | Alarms |
|---|---|---|
| Road-facing ADAS camera | Centre of the windscreen behind the mirror, inside the wiper sweep, level with the road. | Forward collision, headway, lane departure, pedestrian |
| Driver-facing DSM camera | A-pillar or dashboard, facing the driver's face, with infrared for night. | Fatigue, distraction, phone, smoking, seatbelt |
| Side camera | Passenger side, or both sides on trucks, tankers and buses. | Blind spot |
Calibrate after install
Road alarms depend on the camera height and angle. Calibrate each camera after install and after a windscreen change, and keep the record.
What can each alarm not detect?
| Alarm | Typical limits |
|---|---|
| Forward collision warning | Warns, does not brake. Usually works only above a minimum speed set in the device. Can miss stopped vehicles, crossing traffic, and objects in glare, heavy rain, dust or darkness. |
| Headway monitoring | Measures the time gap to the vehicle ahead in the same lane only. Needs a calibrated camera and a speed source. Vehicles cutting in from the side are seen late. |
| Lane departure warning | Needs visible lane markings, so desert roads and worn paint give no alarm. Often silent below a set speed or when the turn signal is wired and on. Does not steer. |
| Pedestrian collision warning | Short range and front view only. People who are partly hidden, small, in the dark or against the light are detected less well. Nothing at the sides or rear. |
| Blind-spot detection | Covers only the zone the side camera sees. How well it detects cyclists and people varies by model. A dirty lens blinds it. |
| Fatigue alert | Reads signs such as eye closure and yawning, not fatigue itself. Sunglasses that block infrared, a cap or a camera angled off the face reduce detection. A tired driver may show no signs until late. |
| Distraction alert | Flags the head or eyes turned away longer than a set time. Mirror checks and glances at a navigation screen can trigger it when the threshold is tight. |
| Phone use alert | Detects a phone held to the ear or in the hand in view. Hands-free calls and a phone held low are often missed. |
| Smoking alert | Detects a cigarette near the mouth and can confuse a pen, a straw or a hand. Does not measure smoke and may not detect vaping. |
| Seatbelt alert | Looks for the belt across the chest. Dark clothes, a belt worn under the arm and night images reduce accuracy. |
| Camera cover alert | Detects a fully covered lens or a very dark image. A camera turned away or a partly covered lens may not be flagged. |
Headway in metres
A headway alarm is set in seconds, but drivers think in metres. At 80 km/h a vehicle covers 22.2 metres a second. An alarm set at 1 second fires at 22.2 metres. The UK Highway Code advises at least a two-second gap, 44.4 metres at that speed.
Gap (m) = speed (km/h) / 3.6 x headway (s)
80 / 3.6 x 1 = 22.2 m
80 / 3.6 x 2 = 44.4 mTwo-second guidance: UK Highway Code, rule 126. Check your national rules and company policy.
Sources and limits
- Two-second gap: UK Highway Code, rules 103 to 158 (rule 126): at least a two-second gap on high-speed roads, at least doubled on wet roads. Source and date checked 2026-11-03.
- The crash-to-alarm mapping, the points and the bands are written for this page. They are indicative, not a safety standard.
- Alarm limits are typical for camera-based systems. Each model behaves differently, so read its manual.
- Driver-facing cameras record people. Give drivers a clear notice and follow your privacy rules.
- Everything is calculated in your browser. If you ask for the emailed report, your answers are sent to our server with the request and kept for up to 45 days.