Motion Sensor Went Off For No Reason

So first, let me tell you that I am not a fan of AT&T. The day that my contract ends, will be a very happy day for me indeed!

That being said, after having this horrible, overpriced service for nearly a year, today I received an alert that my Motion Sensor had detected motion and my alarm went off.

My phone rang and I picked it up and told the AT&T agent, "No one is home, please send the police!"

She replies, "Hello, this is AT&T. We noticed the motion sens..."

I cut her off and told her, "No one is home, please call the police!"

She pauses and replies, "So you want us to send the authorities to your residence?"

I yelled "YES!"

I mean, seriously? Every second counts with a situation like this.

Anyway, my wife wound up leaving work and went home. The police came and there was NOTHING that we could see that could make this thing go off.

I have one pet, a cat. She weighs 11 lbs.
Nothing was distrubed or knocked over.
No other sensors tripped.

I know AT&T has horrible service and equipment, but has anyone else exerienced something like this before? I clean the motion sensor monthly to make sure no dust or cobwebs gather up on it.

And also, why is it that the phone call was the last I heard from AT&T? They don't call again to see if everything is okay? They don't call when someone disarms the alarm after it has been tripped?

Thanks!