Workingonit, you are correct in that there should be a siren there assuming your car had the factory alarm system. I am not sure if any e53 x5s were sold without alarms, but I sort of doubt it. Mine (siren) sits exactly where you describe and is strangely easy to get to, for a BMW!

When I got to the airport today I locked the car and was walking away when whaddya know, the alarm went off. It had been behaving perfectly for several days. It’s the little gremlins that drive me nuts with this car. Fuse 13 is back out… Hopefully the battery in the siren is in fact failing and triggering the alarm, rather than having to start chasing wires for shorts, etc. I considered the motion sensor could be failing, but the alarm still goes off when I double-clutch the key lock to turn the sensor off.

Happy to send you my questionable siren to troubleshoot with if you want, after I get the new one in next week.

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Current
Original owner 2002 E53 X5 4.4i to 4.6i swap
2026 G80 M3 6 spd
2025 G06 X5 50e
Former
1972 Audi Fox
1986 Saab 900S
1996 BMW Z3
1998 BMW E36 M3 Sedan
2004 BMW E46 M3
2006 Audi A3 Quatro
1993 Mopar 318 Jeep Grand Cherokee
2015 V6 Jeep Grand Cherokee