I think my phone will take a photo without bringing up the camera app UI with a certain button combination. But I am not sure if I could make this use the front

I think my phone will take a photo without bringing up the camera app UI with a certain button combination. But I am not sure if I could make this use the front camera. EDIT: I stand corrected, the button combination does not work when the phone is unlocked and it always uses the rear camera. But I guess at least in principle one could build this.