Removed the battery then the alarm went off, and off, and off!

[Cads]

So i realised the battery was dead and went to remove it to save time tomorrow, then the alarm started and kept going off and stopping then off again.
It’s finally stopped. But why did it do that?
Ive left it now with the bonnet up, because I dare not touch anything. Although my phone is in the car so I’m going to have to open a door.

 

[Cads]

It went off once more when I opened the door to get my phone and hasn’t gone off since the door was shut.
It’s an odd one. I’m led to believe it’s supposed to go off when the battery is disconnected but I’ve had the positive terminal off loads when playing with my steering wheel. Maybe keeping the earth connected was enough to prevent this previously??