a few days ago about pendulum divination. Here is Wiki's take on dowsing with a 'nod' to pendulum divination.
A dowser at work, from Pierre le Brun, Histoire Critique des Pratiques Superstitieuses, (Jean-Frederic Bernard, 1733–1736). It is unclear whether or not the dowser is using a diving rod or the lesser known Scrimometer. (From http://en.wikipedia.org/wiki/Image:18th_century_dowser.jpg)
Pendulums can be bought for this purpose or can be made with any object that can be tied and anything that can tie and that is flexible. As with all things, intent is key. The highest thoughts should be brought to all things divine.