Strange behavior from blue light

Hello! I'm new to this kind of forum so please forgive me. My father drives a 4 door 2015 Toyota Tacoma and it's recently ran into an issue I believe you guys could help us out with.

There is a blue light under the driver's side of the dashboard (I believe it's called a theft deterrent light?) that normally blinks whenever the truck is off and locked. I've seen the light from it whenever I look at it. Recently, my father's noticed different behavior from this light. It stays on instead of blinking now. We were unloading some things from the back seat today and the truck was off with the door unlocked. We heard a prolonged beep, not exactly the loud alarm but some other kind of alarm I can't quite describe. It turned off when my father closed the door and had it lock itself.

Could anybody please help us diagnose what might be going on here? My father suspects somebody's tried breaking into the truck or otherwise tampering with it. He has reason to believe so, but could trying to tamper with the doors/alarm be cause for this issue or does it have something to do with a technical issue we may not be realizing? I've tried looking up this issue online to no avail, so your help would especially be appreciated.

Thank you.

 

I've never seen a blue light & believe it must be aftermarket.

 

Definitely aftermarket alarm system. Some are triggered off of the factory keyless entry. If it's on steady, that may be that it's in valet mode. On some alarms, the LED is the valet button. To know for sure what brand of alarm it is, remove the panel below the steering column and look
For a black box about the size of a deck of cards. If you want to test the alarm, leave the window rolled down, arm the alarm, and then reach inside and open the door.