Defender alarm

My Defender is 2011 and has an irritating alarm. I noticed that the batter might benefit from a charge so the following day I went to the vehicle with the battery charger in hand, opened the n/s door and off went the alarm. Fortunately the fob was close by. I tried to charge the battery but each time I opened the door the alarm went off.
An auto-electrician located the horns and said he could disconnect them but would need to find another way of operating he horn from the horn push. A week later I used the vehicle for a 100 yard trip. Parked it, climbed out and then when I tried to get back in to move the vehicle off went the alarm again.
For some reason it keeps arming itself even when it's been switched off. Currently it's sitting in the yard with the red warning light in the speedometer flashing.
Is there any reason for this, given that I haven't armed it using the fob and can I have the alarm removed?

The red warning light indicates the immobiliser status as well as the alarm status. So it will flash when locked with the key (alarm off). Is it the horns which are sounding, or the BBUS (battery back up system) alarm?

Thank you for your response. I am not sure which horns are sounding. I don't lock the vehicle. The driver's door lock doesn't work.

Too much in the way of electronics on these new fangled defenders for my small brain to comprehend ...

Had similar
Check all your points of entry contact switches (the same one that acitvate the lights) Could be sticky or have corrosion due to water ingress, aye water gets everywhere.
Also the one under the bonnet, mine was sticking sometimes and caused the red light on the dash to stay on as well.