Whats that alarm noise in Downtown Houston, always on.?

The alarm has been on all the times I've been down in the are and I've been wondering what it is. It sounds like birds chirping then it turns to a squawking noise then it turns to a variation of beeps like an alarm. I was in the area of San Jacinto and Capitol when I heard but couldn't pin point where I heard it. Its on 24/7 from what I can tell. Anybody know what it is?