Honda civic alarm goes off when I lock the doors. Just had a new battery fitted.

SOURCE: Car Alarm

sounds like the drivers side key switch has failed remove the interior door panel and there will be a switch attached to the back of the key lock cylinder or around there it should be two or three wires also check the door jamb wire harness where the door closes for any broken or damaged wires, use a vot meter and see if you get power or ground to the opposite side of the switch when you use the key to lock and unlock the door if nothing changes and there is power or ground! at this switch i would replace it, i don't think there is one but if the car has a passenger side key hole try to unlock the car from that side and see if you get the same problem -jeff

SOURCE: Alarm haywire, can't override anti-theft system or turn on car

The Alarm on my Mercedes ML320 sounded every night, then it started doing it more often, Showed it to the dealer he says it's the 'Tow Sensor', that needs to be repaced. $700, down the drain. I have already started hating this car, it eats $500-600, every 6 months...

SOURCE: 2001 subaru impreza WRX unlocking doors with key

usually after opening the door you can deactivate the alarm by pushing th unlock button or simply insert keyy in ignition and turn it on.

SOURCE: 2002 VW Golf TDI open door light & alarm

check door switches remove 1 at a time and unplug it once you find the bad switch lights will go out
un plug 1 at a time

SOURCE: can not lock car by key remote . toyota rav 4 53 plate

If your car has an alarm with a separate remote, it is a separate system and it is probably self-arming. When you lock the doors with the key central lock, the alarm gets armed by the RAV4 being OFF and the door locking action. When you unlock the doors with the key, the alarm is still armed because the key is not comunicating with the alarm just the cars factory keyless system.