Originally Posted by
Iride01
If you aren't on a budget, you might also consider a Garmin Varia. My son has one and it alerts for overtaking cars well before they get to you. It even does a pretty good job at alerting for cyclist overtaking you too, but since the unit is doing a comparison of relative speeds, it sometimes will let a cyclist sneak up on you. It's also an excellent taillight.
I'm not recommending it instead of the mirror, but something else to use in conjunction with the mirror.
I’ve used the Garmin Varia radar/light for around the last 4,000 miles. I’ve found it to be 100% accurate identifying vehicles coming up behind me, whether at moderate or high speed and it also visually represents how far back each of the cars/trucks are.
Do I still visually check before switching lanes or turning left? Yep. But I’ve never found the Varia to be wrong. Not once.
I think this is the best safety item after a helmet.