When I got back to the car after taking the dog for a walk, I thought I'd video the sounds made by the car in response to the remote fob.
I replaced the batteries in my fobs probably 2 years ago now. 1 of the fobs never worked again after that as (as Hippo described) the metal clip holding the battery in came loose. The other 1 worked fine for a while but quite quickly the car started beeping at me again when using it. The battery was brand new and sealed, which isn't a guarantee its got good charge, but I suspect the pick-up is as likely candidate for being faulty. The remote always unlocks the car, either close up or from a distance, but 50% of the time it will beep at me!
The video starts with the car unlocked and door open. I press the 'lock' button on the fob and the car's horn sounds. I then press the 'unlock' button (with the worn out rubber) and the cabin speaker beeping starts. You can see the dash led blinking with the beeping as I get in the car. It would normally beep for a bit longer - but as I get in the car I press the 'unlock' button again and it stops.