Probably not a real problem, but if two key-holders are at the car at the same time and one key is faulty (battery) will the car display a faulty signal or not ... If it is the drivers key and he is dropping off the passenger, will the driver still be able to start the car again ... I assume that the trick of holding the key fob up against the stop / start button would work OK to get the car home ... Changing the battery is OK for me as the drivers key (battery) had to be changed after only eighteen months ... Does anyone carry a spare battery just in case ... I think I will in future carry a spare battery in the glove compartment just in case ... It would then be easy to replace the battery whilst in the car park ... This is my fifth Jazz in about 17 years, but the first with this method of keyless entry ... Gotta admit that I like this keyless method but wish there was a warning that would say that the battery needed changing in the next month or whatever.