I could be going crazy here but I swear there was a utility device on the market for (shall we say) "prompting" your on stage helper. It was an audio based device that could say/play anything.....
It used, if I remember correctly, induction rather than a speaker system to get the sound delivered and in the one version I recall it could be also concealed in a TT.
MODS if I'm giving too much away please feel free to bansish this to the bin - everyone else, please reply with the name of msystery item (or you can PM me).
To earn extra points telling me where one can be purchased (if still made) would be great but, I can always google it msyself from there
