During Prohibition, an enforcement agent had a tough job: If he infiltrated a speakeasy and ordered a drink to confirm that it was alcoholic, his oral testimony could easily be attacked in court, and, ironically, once he admitted that he drank alcohol regularly then defense attorneys could question his reliability.
Robert Tetro patented this solution in 1930. Instead of drinking your drink, you’d discreetly clip a tube over the rim of the glass, reach into your pocket and squeeze a bulb, drawing off a sample. Then you’d pay your tab and leave. If the sample proved alcoholic then the feds could raid the place, which had no warning that it was under surveillance. And now the authorities had physical proof that alcohol was being served.
In the patent application, Tetro says his invention “has been used to a considerable extent, proving its value.” He was based in Michigan; I don’t know how widely it was used.