89 240sx tachmeter(rpm meter) acting strange

[1989240sx]

hey guys i just got a security system install in my car and how my rpm gauges go up and down randomly but the car drives normal what could be the problum that would cause this thanks for the help

[180fan]

possible during the alarm installation, something tapped the tach wire.

[omdella]

yea u might wanna check around where the brain of ur alarm is and see if they tapped any of ur rpm lines