Googling 'fake car alarm' got me several options- home-built and store-bought.
Sorry, I don't have time to review any of the sites, just googled it to see what would come up.

Good luck! I hope it helps the problem!
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10101311 (20GB- backup empeg)
10101466 (2x60GB, Eutronix/GreenLights Blue) (Stolen!)