I think a notification to a smart phone if your gun safe is compromised is a very nice idea, although I'd be very surprised if it isn't already available, somewhere. But the notion of a pressure plate inside the safe as the switch/actuator?
Nope. That's fine if you only have one gun, but many owners who have gun safes do so because they have multiple firearms. It's not unusual to find people with 10, 20, 30 and more handguns, and similar numbers of rifles and/or shotguns. Such people would not want to roll the dice on a thief happening to grab the one gun that's on the pressure plate. What's needed is a remote app that sends an alert if the safe itself is either opened or moved.