I can't speak for the puffer machines since I've never gotten to work with one, but the WTMDs can technically be dialed (technically, programmed; there's no physical dial~) up or down. I don't know how it works at other airports, but here the keypad to adjust the settings of the WTMD is locked, and nobody at our airport has the key. At all.

The last time it was messed with at all was back in 2003, and the sensitivity was toned down by about 30%. Don't know who the guy was who came to do it, don't know who he works for (though an educated guess would say SIEMENS, since they handle the upkeep on the rest of our equipment), and I haven't seen him since.