MS18A motion sensor malfunctioning

[dfc37]

I've had my current my current x-10 system in operation for over two years. One of the MS18A motion sensors recently started setting off the alarm within seconds of arming in away mode.  The activated sensor displays on the SC12A console. Removing the affected sensor zone from the console allows the system to be armed in away mode without event. I attempted re-installing the MS18A and the problem returned. I relocated the MS18A to a location where there was no heat source or possibility of motion to be detected and the problem persisted. I re-tried initial sensor setup and installation multiple times with no change. I observed the sensor from a 90 degree angle, out of the sensing range, and noticed the green LED flashes every 30 seconds even when there is no possible movement. Is the sensor faulty or is there a fix? The system works normally with this sensor removed from the system.

[HA Dave]

....... the green LED flashes every 30 seconds even when there is no possible movement. Is the sensor faulty...?

Yes.

[Brian H]

You did try a fresh battery?

Can you see inside the sensor and look for something like a spider crawling around?
I had a smoke detector trigger and out popped a spider. 

[dhouston]

I had a smoke detector trigger and out popped a spider. 

About 15 years ago I had a spider take up residence in a slight depression on the front of a plug-in module. It's been too long for me to recall details of the module but the spider stayed for several weeks so I'm guessing there was something about it that the spider (or its prey) found attractive.