Also used to use them for....
... a very sensitive diaphragm in a simple "dispstick" device for finding the level of Liquid Helium in a helium-dewar-inside-a-liquid-nitrogen-dewar flask.
We made a long hollow tube of 3mm stainless-steel tubing stock and welded a 5cm "cup" to one end. Stretching a condom over the cup and keeping one's finger on the tight diaphragm, the tube was slowly lowered into the flask. When the end of the tube got to just above the liquid helium, a definite movement of the diaphragm could be felt. The depth of the tube at that point yielded the amount of liquid helium in the dewar.
Of course, the sudden cold tended to damage the condom after just a couple of uses* and so we went through a lot of condoms. This was in about 1970 and condoms were still kept hidden and had to be asked for. University rules prevented ordering them directly ("You want a gross of condoms for what!?") so we snuck them through on petty cash. We'd always send Linda, the prettiest female grad student (and best sport) to get them. It would always cause quite a stir when she went in and asked for her "supplies!"
* uses in this application, anyway.