side effects
In the early noughties I worked for a company where we had fingerprint scanners at the doors. More for show than for real use (we were some kind of demo lab, and the parent company tried to sell them). They didn't really work if your fingers were dry or cold. So we learnt to blow at our finger before we entered. At least I thought we had learnt that, until one winter morning I entered behind a guy who stuck his finger into his mouth before pressing it on the glass. I don't remember if we all got the flu at the same time...