external antenna with alarm system

I am a ham radio operator so I have several antennas mounted into the roof of my truck. I will soon be buying a viper alarm system... I'm wondering if anybody has ever had an external antenna for their alarm system? I know it would be a point of failure since anybody can remove the antenna by hand. I would torque the antenna down so you can't remove it without tools. Nobody is going to see a quarter wave 900mhz antenna on the roof of a lifted truck anyway.

My truck is a 2008 Toyota Tacoma double cab with a 3" lift and 33" tires.

In theory its fine the antenna to use would be a European GSM because we use 900mhz, the US uses 850mhz. In practice the extra gain isn't worth the effort.