I have two pixel 5a phones with GrapheneOS installed. I have a major usability issue with both of them in that when in my pocket, it will unlock the phone if the fingerprint touches the sensor.
On old phones I've had such as OnePlus6 with LineageOS, if the screen (and ambient display) is off due to the proximity sensor detecting the screen being covered (which is always the case when in my pocket), the fingerprint reader won't do anything. Also, if the ambient display is on with the OnePlus6 with LineageOS and a wrong fingerprint is scanned, it will just say "Too many attempts. Try again later." and not enable any touch screen functions and won't turn the full screen on (it just stays in ambient display mode). This prevents accidental unlocks (or emergency calls, flashlight on, etc.) being made when picking up the phone from a surface and the proximity sensor is not detecting a nearby object covering the screen.
With Pixel 5a with GrapheneOS, it seems to ignore the proximity sensor and use fingerprint unlock at all times. This is a major usability issue as the phone gets unlocked all the time unintentionally when in a pocket.
If I try to always put the phone in my left pocket and only have a finger from my right hand programmed for the, this still doesn't work because GrapheneOS seems to turn the screen on and bring up a PIN unlock screen after touching with the wrong finger, then the touchscreen is activated and emergency calls can be accidentally made and the flashlight and other things can be changed.
I do know that the proximity sensor works on the Pixel 5a because https://f-droid.org/packages/com.kgurgul.cpuinfo/ allows me to look at sensor values and the proximity sensor does detect nearby objects. Also, the screen turns off while making a call. Also, placing a post it note on the top of the screen causes the ambient display to turn off after a few seconds. Also, I have the same issue on two pixel 5a phones with GrapheneOS.
I'm trying to figure out if this issue is specific to the pixel 5a or if other pixel phone models do it to. Also, I don't know if this is a GrapheneOS issue or if this is how Google Android behaves as well. I also don't know if this is something that can be fixed with software or if it is somehow a hardware limitation.
Is there some kind of setting I might have enabled that has caused this issue?
If this is a bug, it would be great if it could be fixed. Also, it would be nice to have an option for the fingerprint reader to not ever do anything at all unless the power button is pressed first and the proximity sensor detects no object. This would prevent even more accidental unlocks when outside of the pocket. I don't think it is too hard to press the power button quickly before attempting to unlock with a finger (if you want to).