I had a similar problem with an Alpine Alarm. Turned out that the brain had gone bad and they replaced it under warranty.
They gave me this weird sunspot theory or something like that to explain the brain failure. What ever. Have the shop that installed it take a look at it. I usually do everything on my cars myself, but aftermarket alarms I won't touch. They go crazy pretty often and can leave you clueless if you installed them yourself.
81 300 SD grey/palomino 168K miles
84 190E 2.3 black/grey 64K miles (wrecked)
85 190E 2.3 maroon/palomino 92K miles
88 300E desert red/palomino 204k miles
(made to look like a '94-95)
92 400E desert taupe/creme beige 120K miles
(converted to 94-95 E420 looks)