I'm pretty sure it's telling you there is a problem with the switches, not the "sensors"

Those 3 switches (41, 42 & 43) are in the King's Chamber in the backbox. They are either stuck closed, misadjusted so they won't close when triggered, or simply haven't been hit in a long period of time. Go into switch edge test, manipulate the switches manually and see what happens. Adjust the leafs as necessary. If that doesn't look like the problem, check that the wires are intact, etc.

Everybody else is giving you good advice on the drops - although if it's dirty, take it apart and clean it correctly. Don't spray stuff into it.