It isn't a car alarm....
It is some form of tracker, but not the conventional sort. More the sort fitted to delivery vans so the "man" knows where you are, how fast you have been driving, and so on.
From their website....
"Avonwood supplies a range of identification systems based on both active and passive RFID technologies as well as developing a range of niche innovative electronic solutions.
Primarily targeted towards safety, security and asset management applications"
This is a bit of a concern...https://avonwood.co.uk/eureka-discovery-systems/
I am assuming you are not the first owner. If I were in your shoes I'd want it removed, pronto.
But removing it might cause other issues.
So first call is Avonwood, and if it costs money to have it removed, the dealer, or the previous owner.