my daughters car alarm keeps going off for no apparent reason and all hours day and night.
Aftermarket alarm or a manufacturer equipped? If it's OE then more than likely there's a problem with the body control module, or a problem with one of the switches or wiring in a door/hood/trunk. Basically what's happening is one of the switches is making the car think a door (trunk or hood) opened and setting the alarm off. Or the module that controls that system is failing. Moisture, humidity or age can cause these problems. If it is one of these problems, sadly enough you're going to have to take it to a shop to have it diagnosed. Other possibility, a weak car battery (2008 would have a 6 year old battery in it if never been changed, even if that's not the culprit I would recommend a new one especially before winter [if you have those]).
Search Dodge Avenger Questions
Dodge Avenger Experts
Related Models For Sale
Used Cars For Sale