Pulsate voltage on/off

I am attempting to wire up a gsm relay switch as a project. I will wire the output to a spare key fob. I can specify how long the signal from the gsm relay will be on. On my key fob I have to hit the lock button 3 times within 4 seconds to start the vehicle. I will set the relay to remain energized for 4 seconds. What I need to do is once the signal from the gsm relay is on, I need to be able to pulsate it on/off 3 times at 1 second intervals. So, how can I pulsate the signal from on to off and repeat that 2 additional times?