Want to build a difficult to reset alarm

I want to build an alarm for a small easy to pick combination safe and our backpacks in our house. I would like to make the alarm so that a small pin is removed from the circuit and once removed, it is very difficult to reset the alarm (can only be reset by me). Possibly a combination would have to be entered to reset the alarm. The reason I need this is because an adult family member in our household goes through our stuff on a regular basis and steals from us. I have used webcams with motion detection software and caught him in the act of going through our stuff and stealing and that humiliation of seeing himself on video and the fact that the webcams are always on has now detered him from stealing in those areas, but we have other areas of the house that do not have webcams. While we sleep or work he goes through our backpacks, drawers and other stuff stealing money, medicines and generally everything he can get his hands on. My wife used to have a device that you could put on a closet door and when the door was opened it pulled the pin. That device was very basic though and if you put the pin back or got a small screwdriver and removed the batteries you could turn it off. He actually put the pin back but could not set the alarm device back up on the closet correctly so we still knew it had been activated. That device eventually quit working. I am into retro gaming and a few years ago I took an old Commodore 64 with the joystick and hacked the joystick. I connected a magnetically activated alarm switch to one of the joystick switches and plugged the joystick in. I put the magnet switch on a drawer we have in our bedroom and I wrote a program that kept monitoring (simple PEEK command) that joystick port and when there was a value change of any kind it triggered an program loop that played an annoying alarm sound and wrote "INTRUDER" on the screen which also flashed colors. The program could have been stopped by the Commodore Run/Stop key, but he did not know that. Sure enough, the first day we got home from work and it had been triggered. This was when he was a teenager. My C64 is no longer working and I need to come up with more clever stuff now and something that will fit in a backpack. Any suggestions or schematics you can point me to? Kicking this person out is not an option at this time.