The curious case of missing rubbish boxes

On a recent road trip in Tohoku, I noticed a sign on rubbish bins in most of the parking and service areas in Iwate, that both interested and horrified me. The sign is specifically on the small sanitary rubbish bins in the women's toilets. The sign says, in both Japanese and English:

Security system in operation. If this box is taken out of the facility, an alarm will sound.

It took a while for the penny to drop, so to speak, as to why there are such signs on the rubbish boxes. And it came to me, because I remembered seeing similar signs in toilets about toilet paper, when there was a spree of toilet paper stealing in Japan about 20 years ago. The toilet paper wasn't alarmed though!! So it dawned on me, that unfortunately, much to my horror, there was probably a bout of rubbish bin theft in the toilets on the Iwate stretch of the Tohoku expressway!

Why else would they feel the need to go to such lengths. And who on earth would steal sanitary bins and to what purpose? I doubt it was just one that was taken - surely that wouldn't lead to all the bins having alarms put on them? What was the person / people doing with them - selling them? If so, how gross, selling a used sanitary bin! Maybe there is another reason they are alarmed - any idea!?