Yaris Central Locking Problem

[pbasuita]

I have a 2004 reg Yaris that has developed a problem with the central locking. It keeps relocking itself every few minutes after it has been initially locked using the remote. Its fine if the car is not locked - the problem does not occur then. The problem has got worse over time. Initailly it was every few minutes, now it relocks within less than a minute. Have had to disconnect the battery to stop it.

I have tried moving the car to a different location, and taking the battery out of the remote. Problem still occurs.

Any ideas anyone ?