Did they do any damage to anything?
Did they not just use some jumper wires.
I would do such a prank as long as it caused no damage.
A friend told me that in Osaka, Japan, during the U.S. Military occupation after WWII, they had a device on base which sounded at 12:00 and 16:00, SIR! (That's Noon and 4 p.m. to all us dummies.)
The timer had a swinging pendulum which had a sharp point on the end which dipped into a small pool of mercury. Each pass would close a circuit and relays would count the swings.
The siren had three horizontal exponential horns covering 360 degrees.
10 hp three-phase motor. Sounded at 400 Hz.
A Federal Signal Siren?
At 02:00, he heard the compressor start.
He ran to the building to disarm the alarm, but knew he could not get to it in time. His partner, also involved with the timekeeping device, also showed up out of breath.
Fortunately, the prankster did not know how to set the other timer to open the valve.
I would have figured it out and had a blast.