Another possibility is water in your trunk. Underneath the hard foam block in the floor of your trunk (passenger side) is an alarm control module as well as your central locking module. Under the car and covered by undercoating is a round rubber plug about the size of a dime. There is one for both trunk tubs, at the lowest spot. Clean away the undercoating and pry the plug out. If any water comes out you've got two problems. First, you have a leak. Second, your modules will be damaged and are very expensive to replace.
Its worth a look.