A bike radar is a rear light with a small radar sensor built in. It watches the road behind you and sends alerts to your bike computer or phone when a vehicle approaches. Here is what it does, what it does not do, and what to check before you buy.
Short version
- Radar warns you that something is coming. It does not tell you whether the driver has seen you.
- You need a screen to show the alerts: a compatible bike computer, or a phone app.
- Check compatibility with your computer before buying.
How it works
The unit mounts on your seatpost like a normal rear light. Its radar detects vehicles behind you and estimates how fast they are closing. Your bike computer then shows a dot for each vehicle moving up the side of the screen, usually with a colour change for faster approaches and an audible alert.
What it does well
- Gives early warning on quiet roads, where a car can arrive faster than you expect.
- Lets you hold your line with confidence, instead of looking over your shoulder.
- Doubles as your rear light, often with modes that brighten when a car approaches.
What it does not do
Radar cannot tell you a driver’s intentions, and it does not replace looking behind you before you change position on the road. In heavy traffic it will show constant alerts, which is less useful than on open roads. Treat it as an extra sense, not a safety guarantee.
Before you buy
- Compatibility. Check that your bike computer supports the radar’s alerts (many use the ANT+ radar profile).
- Battery. Compare the maker’s run-time for radar plus light, not radar alone.
- Mount. Make sure it fits your seatpost shape and sits clear of a saddle bag.
We will publish our own side-by-side tests once units have been through our hands. Until then, see the lights and radar we stock, or ask us which radar works with your computer.