One of my old units had that problem - open access, stuff going "missing".
Some managers were bought in from other units to run things for awhile, one of the first things they did was photograph everything & told everyone that the first time something disappears they would call the police in as a first step.
Funny the stealing stopped! And gear suddenly re-appeared. Then when I took over, got rid of the people who weren't quite up to speed/ or unsuitable for our type of work - never had a problem since! Not sure if the the two are connected, or just an amazing coincidence
Swipe cards are a good idea - but very expensive to set up initially.
Anyway good luck with it, it's a pity that some low lifes stuff everything up for the decent silent majority.
cheers