I have the Varia paired with a head unit for the visual que, but also have the mobile app open on my phone in my jersey pocket. The phone is paired to a bone conductive headset (Shokz) and I receive the audible alert of when a car approaches and passes. You could also get a visual que from the mobile app if you mounted your phone on the bars, but I prefer it to be tucked up in my pocket.
Good luck.
Mike