There are a range of tactics to be used before going to key operated call points. These include fitting secondary "screecher " covers to call points so staff are aware of interference, moving call points to positions where they are visible, use of CCTV etc. to catch culprits.
If all this fails to bring the false alarms under control then a delay with a proper system of investigation is a possible runner. I know of at least two external bin fires set as arson attempts, alerted by the break glasses which would not have activated the auto detection before the roof overhang had caught.
I also know of a school which went down the key route. The nice visiting Fire Officer asked staff for a key. Six members of staff later and a key was finally produced.
It is also sod's law the areas with most false alarms seem to have the most arson attempts.
(Based on experience in East London)