Is Anand possibly cheating (the metal detector)? While I write this question, I am certain I completely miss the spirit of the world championship. But however, I got curious about how well the cheating-countermeasures at the championship actually work.

Before the match, I watched a TV program which explained how the games would be, and they showed us a metal detector that the players had to go through before every match. The purpose of the metal detector was to find devices that could be used for cheating.

In today's match (number 7), I notice that Anand is wearing his wrist watch. I would believe this would trigger the metal detector, and I doubt they would dismantle it to check if it's ok.

Since the metal detector is a countermeasure to cheating, should they let devices such as wristwatches pass?

I seriously doubt that anyone would cheat at this level - I cannot imagine the impact it would have on the game (their career).
The organizers certainly noticed the watch, if you did. Therefore, since it was allowed at the match, they must have determined that it could not aid chess play in any way.

Their reasoning should be simple: either the watch communicates with an outside device in order to signal the player, or else the watch does all chess calculation itself.

Communication with an outside device requires radiation which is easily monitored by a counter-cheating system, and a watch that could a) internally calculate chess moves at such a strength as to aid an elite human, b) accurately yet undetectably signal the wearer from an analog clockface, and c) accurately read the chess board, is currently technologically impossible.

Hence, dismantling the watch is unnecessary until technology allows undetectable wireless communication or a computer of the described caliber becomes even a remote possibility.