Shock sensor mounting

Do you mount your shock sensor with screws directly to firewall?

Or do you simply zip tie it to some bracket?

And why?

When I got my alarm installed for me the installer screwed it to the steering column.  This didn't work for me at all.  It only sensed the front drivers fender, nothing else.  I relocated it using zipties to an air vent.  Now it works perfectly all over the car.

The only problem I face now is when people with loud music and a LOT of bass come by, the vibration triggers the warn away of the shock sensor.