I'm attempting to replace my alarm module and have successfully got to the metal box, removed the nut and bent the metal to access the unit. I'm having trouble with the nut/bolt pictured. As I'm turning the nut the bolt turns with it. Does anyone know what's on the other end of this? As far as I can tell it is (or at least is supposed to be) somehow attached to the alarm module to hold it in place. Is it just a standard bolt that I can replace if I break it trying to remove it with brute force, or is it something more specific that will be harder to replace?

It is a bolt slid into a retaining recess of the plastic of the siren on the other side. If it is turning the bolt has seized and has probably worn the plastic retaining slot.

 

You know the sirens that come out faulty usually have damaged pcb due to the battery cell leakage?

 

Few options. Spray it with penetrating spray, Impact gun maybe, grind it off or use a bolt remover kit to drill into the end of the bolt to try to counter hold it.

Thank you. I've got a new siren on the way, I've seen a few other threads on here discussing them and decided the easiest way forward was to buy one from China as recommended by a few other people on here. If its just a plastic recess on the back of the old siren I'm tempted to see if I can pull it hard enough to snap the plastic so I can then get a spanner on each end of the nut and the bolt head. No great loss if such a primitive approach destroys the old siren, given the circuit board is likely to be damaged anyway

Try wire brushing the bolt threads, apply penetrating fluid then counter hold the exposed thread with good grips while using a spanner on the nut.

 

If you get it started and run out of grip try a flat screwdriver to pry the nut away as you turn the spanner, the increased tension on the bolt can stop it turning.

Have at it with a hammer or other destructive tool of your choice, you have a new alarmon order anyway.

 

My AliExpress alarm module sent the car to Coventry!

This nut holds the alarm into the metal protective box, you can undo the other nut and bend it all downwards giving you some room to hopefully get some purchase on it.