ISO: A gadget that will attach to a door, sending a notification when it opens

I work in a group home. I'm suspecting one of my residents has a key that was lost by a staff member, and is using it to get into the storage area where medications, snacks and sensitive documents are kept. I'm looking for a device that would discreetly send a notification when the door is opened, or any other solution aside from hiring a security guard. Is there any device that one in this community would recommend to me?

Thanks in advance

cycloptishred

A door sensor of some sort... there might be a model that will do what your asking. If not then you'll need a way to send the notification, possibly a job for something like a raspberry pi? But, I'm not certain as to the capabilities of these so take my suggestion with a grain of salt (I'm just throwing out ideas that hopefully aren't completely misinformed). Additionally, I assume you'll want a way to turn the notification off during certain times? someone who knows more than me could help point you in the right direction.

Professional would be a door alarm with a sms gateway - IoT for the win.

DIY I would get a normal reed door contact which is used by alarm systems for doors and such, and wire it to the GPIO of a raspberry which than, when the contact is dissenaged (aka. open) will send you an e-mail notification that the door has opend at xx.xx o'clock and even when its closed again.

Or just an alarm system with door contacs, motion detectors and window break detectors (eventualy)
Then you are pretty much covered.

is there anywhere to discreetly mount a security camera where you are?
im sure a cheap one will work fine if hidden well

Spys would leave a small hair on the door knob. There is also a blue dye used in valve lapping that stains the skin for a week. In the Navy the master at arms would put some on a wallet to catch a thief. The guy with the blue hand always seemed to trip and fall on the way to the brig:)

Occam's razor states that the simplest solution is often the right one. I'm considering a camera that captures motion reactive still frames. Can't believe I never thought of it.

Yea that'd be the better solution, plus its more condemning if you ever take the person to court. Rather than just saying "Hey look I got this notification that the door was opened" you can just show the footage.