Garmin Varia RearVue 820 review: by far the best radar light you can buy, but you'll need a recent Garmin GPS to get the best out of it

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Garmin's Varia RearVue 820 is more accurate than any other radar light available, although you need to pair it with a recent Garmin GPS or Garmin’s app to get the full extent of the new features. 

The RearVue 820 is by far the most expensive radar of the group I tested at £259.99 / $299.99 / €299.99, but it’s also the one with the most up-to-date hardware. The light has a very bright 100-lumen output, and with a large-capacity battery, it features a maximum claimed run time of 24 hours. 

The Garmin also has the widest detection angle – 60 degrees – of any radar on test, plus it’s able to determine vehicle sizes, with the graphic depiction on a Garmin head unit showing the type of vehicle, from motorcycles through to cars, vans and trucks.  

Garmin claims the clever programming maintains detection even when other vehicles are travelling at the same speed as you. Many of its rivals, and earlier Garmin radars, suffer from vehicles disappearing from detection when they are moving behind you at the same speed. 

The biggest difference is the protocol Garmin employs to ship data to your head unit. Instead of using the ANT+ radar protocol, the RearVue 820 uses a secure Bluetooth connection on newer Garmin head units, such as the 840 Solar I tested it on. This means you get plenty of functions not seen on rival radars.  

Instead of standard dots depicting traffic, the 820 detects them as different-sized vehicles, as well as placing them in lanes, so not only do you know how far away they are but also where they are relative to you. 

The 820 is claimed to be able to detect vehicles 175 metres (190 yards) away. The ANT+ radar-compatible rivals here claim a potential 190 metres, but in testing none had a detection range close to the RearVue 820’s. According to Garmin's My Bike Radar, the 820 maxed out at a more-than-impressive 192 metres. 

If you don’t have an up-to-date Garmin Edge unit, or use a rival from a brand such as Wahoo, Hammerhead or Bryton, the RearVue 820 will use ANT+ mode, meaning you will get the extended detection and non-disappearing cars (when they're travelling at the same speed as you), but not the granular vehicle sizing and lane detection. 

Garmin Varia RearVue 820 setup 

There’s little to set up with the 820 if you use a compatible Garmin head unit. It’s simply connect and go, because everything is handled admirably by the head unit.

Non-Garmin users can sync the radar with the Garmin Varia app to alter device settings and light modes, and use the phone as a display for the radar.  

Connection via a non-Garmin device or older Garmin is via the ANT+ radar protocol, so it works the same as any of its rivals here, meaning you don’t get the traffic-size detail or lane positioning. 

Garmin Varia RearVue 820 fitting 

The bracket features a Garmin quarter-turn mount, and it comes with a selection of inserts for round, flat or aero posts, along with different-sized straps. 

It’s a solid and stable fit, and being able to leave the bracket on a bike is handy. There are also plenty of other options such as saddle-rail mounts, making it easy to fit to most bikes. 

Garmin Varia RearVue 820 performance 

On the Garmin Edge 840 Solar, the radar performance is brilliant. The side-strip radar view on data screens shows how quickly it detects vehicles. The addition of vehicle sizes and warning triangles on faster-moving traffic is excellent, too.  

Switch to the dedicated radar screen and you see a wide multi-lane view that positions approaching vehicles across the road. For rural riding, this is superfluous, but head into a city on a commute and it’s superb when you hit multi-lane junctions or roundabouts, or when bike lanes bisect multiple traffic lanes.

Having a good indication of where approaching traffic is positioned on the road certainly makes me feel safer, especially in rush-hour traffic. 

Like any radar, it can get overly busy on-screen when riding in peak traffic. Impressively, though, it doesn’t suffer from same-speed disappearing vehicles as its rivals do.  

The radar range is impressive, and I had zero false positives, even when riding through tunnels that tripped up other radars on test. 

The light has ample power, and the run time on solid has exceeded 14 hours, even when riding in heavier traffic, where its clever detection increases the brightness to make you more visible.

It also functions as a brake light – and you can customise the brake light as solid or flashing via the Varia app. 

It doesn’t have as large a light lens as the BBB or Wahoo radars I tested, but the well-positioned LEDs give good all-round visibility, including from the sides.  

Garmin Varia RearVue 820 bottom line 

The RearVue 820 is by far the best bike radar currently available. The clever software eliminates the major bugbear on all radars regarding disappearing same-speed vehicles.  

Its visual positioning of traffic behind you is very useful on multi-lane city roads, and its unique vehicle-size detection is also a standout that is only native to Garmin head units, and x40 and x50 series Edge computers.

If you are a Garmin user and looking for a bike radar light, there isn’t anything better.  

However, it's considerably more expensive than its rivals, although the older Varia RTL515 is still better than Garmin’s four rivals here for radar performance. If you can’t stretch to the RearVue 820’s price tag, shop around for bargains as the RTL515 gets phased out.