I installed the "Sensor" app and after restarting the phone, I noticed when I opened the keyboard, pressed the on/off switch, or touched the camera button, the bottom row of symbols would light up, but the screen remained black. And, touching the buttons at the bottom only caused them to light and nothing caused the screen to come back on.
I took the battery out, and restarted. Got the screen back and uninstalled the app.
I have no idea why this happened. I am sure many use this app with no problems. But, it threw a little scare in me...enough to remove it.
Just passing along what happened.