Or by doing even a slight amount of encoding of the IR signal. Transmitting a single byte as a key (set by region, same as fire dept. elevator keys) would be enough to prevent people from using their TV remote controls or whatever to trip the preempt sensors.

That being said, this is kind of a non-issue already, I have heard a story about someone abusing the preempt sensors like 10 years ago and never since then. Maybe there already exists an encoding scheme.