Connectivity problems usually point to the phone/Bluetooth and not the device.
CarBack connects unfalteringly to the excellent iGSPORT iGS800 computer, with dedicated green/red visual for safe and close-by presence of cars. Having said that, I have heard of a few instances where earlier iGSPORT computers — like the iGS630/630S, do not have a persisting connection. This can happen with any Bluetooth/Ant+ device. This may be solved by clearing the phone's Bluetooth cache, by doing so, effectively resetting all Bluetooth connections the phone has logged. Once that is done, then pair-up the CarBack through the iGS computer sensors menu (do not pair via the phone — the app will do the pairing with the phone as a background task once the connection has been established).
Garmin had better watch out. The CarBack is a very serious heads-up and its trump cards are brightness and a smaller footprint.
Future improvements I'd like to see on the CarBack:
1. Side visibility; the green "battery gauge" is not effective as a presence marker as much as a red light e.g. flashing;
2. Correction to the detection distance. It is not 240m, but 196metres, on account of the functional restriction of Bluetooth/Ant+ technology with radar. TREK has published a piece of information about this on their FAQs page.
3. A brighter light with more modes. The Garmin Varia has a 65 lumen light; the Magene, a 20 lumen and the TREK CarBack, impressively, lights up at 90 lumen (same as the TREK Flare RT tail light).