Problem With Alarm On My 99 Is 200

[atacam]

OK I'm not technical so please bare with me.

Parked up the car last night, nothing unusual, locked with the fob, OK and I went in.

Came out this morning, unlocked the car, with the fob and noticed it took a second or two for the lights to blink.

Went to start the car, the alarm went off.

Hit the lock on the fob, after a short pause the car alarm stopped and car locked but no lights blinked

Tried it a few times lock, unlock, and the same.

When unlocking the car there is a pause then the lights blink and the car unlocks, lock it, no blink but I can hear it lock.

If I put the key in the ignition, the security light goes out as normal, but the alarm goes off if I start the car, but turns off after 10secs.

I also noticed that there is a capital 'E' where my temperature should be and the fuel gauge is reading empty with the petrol light blinking like a madman, although I know I have about half a tank.

Changed the Battery in my fob, no change. Checked the petrol filler hole and wiggled the white collar inside, no change.

It's almost like the car thinks about unlocking then does but doesn't switch off the alarm.

Any ideas at all please? :(

[atacam]

OK little follow up. Just took out the Battery and found it to be very low and in need of charging. I did also notice that the on auto the lights stay on and the car is saying that a door is open, when I checked them all and they are shut, boot and bonnet too.