A friend of mine had an alarm clock with big rubberized wheels on it that would drive around the room as it went off, so you had to get out of bed to turn it off.
That lasted a few weeks before he grabbed it and chucked it as hard as he could against a wall while still half asleep, then went back to sleep.
The real deal use radar/lidar sensors, so you can replace the whole sensor suite with 4 90-degree sensors facing upwards with the added benefit of being able to track not just range but speed and trajectory.
Slap the computer on the back of the helmet, and it'll even work as a counterweight for the night vision goggles!