Problem with locks on hawkeye WRX

[VictoriaYorks]

I've been noticing for a couple of weeks that I sometimes had to press the key a couple of times for it to register and lock, I presumed it was the battery that needed changing.
As I've parked up today and locked it, instead of the usual 4 clunk noise the locking mechanism makes, it only made 3 noises and when I tried the door it was still unlocked. It worked after another press though.
Has anyone else had this issue?