I am pretty sure that the TVSS is a passive system that automatically arms.
I believe that the control unit for the TVSS is under the driver or front
passenger seat.  You can try unplugging the wire harness from the ECU but it
would probably disable the keyless entry and may prevent the car from
starting.  I would investigate why the alarm is going off only at night.  It
may be doing its job and someone may be messing with the car.

You can install a switch to disable the horn, just remember to turn it back
on when you start the car, or if you know how to read an electrical wiring
diagram, you can try powering the horn from a switched circuit instead of an
always-hot circuit.