'03 Impreza GX Sport - Key fob not working?

[iwishihadanae86]

Rather recently, I purchased my black Impreza. I was rather chuffed and I'm in the process of restoring the car from having a rather pointless bonnet scoop (this is a non-turbo) and getting rid of the rather deafening exhaust. I'm starting to go a little bit off topic, but that's for another day perhaps.

Anyways, a few nights ago I used my key fob to unlock the vehicle to get a few things out then locked it using the key. No problem thus far. The next morning, I went to go and unlock my Subaru and oddly enough the key fob wasn't working? So I tried to enter the vehicle using the key manually however this set off the alarm. I then tried to relock the car again using the key, but the lock could not rotate clockwise or anti-clockwise to lock/unlock? At this point, I could only assume that it was to be the Battery within the key was depleted. I had ordered some new CR1620 coin batteries and replaced the previous one the following day. I went to my car assuming that this was to be my solution to the problem, yet the key fob was unresponsive. So while I was at work, I left the job to my brother who ultimately got fed up with the alarm whining in his ear and it transpired he had also unplugged the Battery and continued doing something counter-productive.

At this point, I am speculating that it may be the immobilizer, or it may be something else. I am unsure if the car has a third-party anti-theft system as the previous owner did not disclose that.

I am in fact learning a new thing about this car every day at this rate.