IXLR8

While working on the clutch slave cylinder these past few days, I noticed that the security alarm horn is emitting a faint hum constantly.

So today I unplugged both horn terminals and took a few measurements...

The brown wire is ground, so lets forget that one.

The hot wire was sitting at roughly 3.25VDC and 1.25VAC (I didn't have an oscilloscope handy). The readings are the same alarm off or alarm on; it made no difference.

What is that all about?

Are they putting a small signal through to verify if someone is tampering with the horn?