Physical harm
@vahnj Yes, I think about this a lot, and while I do not trust those sensors with the future possible functional capacity of my arm, I know that the motors they use to close the doors aren't powerful enough (by design) to cause me more than a nasty bruise if that sensor fails.
Even so, I avoid putting my hand all the way through just in case the worst possible thing happens; I just press on the side of the outer door. ^^;;;