seems strange consdiering on my car (when the power sounder was disconnected) if i used the key in the door the hazards went off when the door was opened until i turned the ignition. reconnecting the power sounder confirmed that it worked, because if i did the same again it would sound and the hazards would flash until i turned the igntion.
Having changed the battery, are you sure the battery holder in the key is soldered to the board? and also, that the two buttons are functioning?
My RCL stopped working, and it was because the battery holder terminals broke. VX wanted £180 odd for a new key, but i send mine to a seller on ebay would put a new battery holder and 2 new buttons on my board for £10!! A year later all is still well!!