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This is one of the all-time best-selling sight gag:

The Human Antenna- Physiological Signals Measuring and Wireless Transmitter (Just Ignore the non-sense).

These comes with a pair of device each with a strong sucker cup with a retractable metal antenna that can be stuck on your forehead for the ultimate mind reading act and any comedy mental play. Stick one on your spectator's forehead and one on your own and ready to go!

No batteries required!

Just pure fun plus serious magic.

Or just serious fun.