Go to Sandtrap forge and spawn a spartan lazer.

It takes good timing. Aim at one of the towers and start charging.

Right as it fires go into monitor mode. If done right you should (every once and a while) hear random spartan lazer shots as long as you stay in monitor mode.

If you hear loud short explosions then thats the towers shooting at you.

They are very inacurate so they shouldn't actually hit you.