First, the method of message transmission. An "accomplice" can send in the moves via morse code silently using this app:
You can get this smartwatch today from Lelong.com.my @ RM 51.99. It will serve as the receiver of the moves in morse code via vibration. Yes it has a vibrate function and it even has bluetooth and 3g (with SIM card!) for communication. And yes it's actually an Android phone just smaller in the form of a watch so it can install the morse code app.
Also, the watch needn't be worn on the wrist and can be hidden in the pockets or on the ankles where the vibrate function is still effective.
I am not advocating cheating but just showing it is so easy to cheat in today's chess tournament. So the metal detection during the recent Women World Championship is not excessive and is in fact quite necessary to deter any form of cheating.
However I don't think smaller, local tournaments such as our own Malaysian Open, Selangor Open, Penang Open, Johor Open will ever use metal detectors. But the question is wiill they start when one cheating incident is discovered?
However, the above is only one of many ways of cheating. I am sure there are other more ingenious and harder to detect methods. (eg: hidden communication devices that will not trigger metal detectors). The method advocated here can easily be circumvented by maybe disallowing spectators, delayed live telecast, body checks and etc. But it does seem a little excessive doesn't it?
also since it is Android based, there are many chess engines that can be run directly off this types of smart watches.
So the need for an "accomplice" may be moot.
Related:-Case study of cheating using in-ear hidden ear piece. (ChessBase article)