Our crew had a good start at stealthing the mission, taking out all the guards and controlling the civilians. However, when we broke the first display case, all our effort was for naught since it triggered the alarm and our escape vehicle took off.
Is there a way to disable the display case alarms?
You can disable the display case alarms in the diamond store heist by using the keycard that you can find on the store manager on the display case alarm panel;
The location of the keypad is random, so far I've seen it spawn in the security room, by the stairs, and in the offices upstairs.
I recently completed the Diamond Store solo stealth and I can confirm the alarm always spawns. You need a keycard to disable it. You put the keycard in a small device on the wall like the picture on the answer above. The device can be spawned in a number of places:
Of course once you have found the device will need a keycard to disable it. You can find it on the manager. She is the only civialian that walks upstairs. She is a woman. Once you have disabled the alarm you can ECM and control the civialians.
I have done this heist for a while now and its always has spawned either in the upstairs room and the security room, but recently I found out it can actually spawn in the store, so my suggestion is bring an ECM jammer.
