Looking for Fluorescence
A majority of diamonds have something called fluorescence, whereby they give off a colored light when exposed to UV rays. You need the room to be dark if you want to find your diamond this way, so turn off the lights first.
Using Hands and Feet
Diamonds have one thing going for them: they are sharp. Feeling around with your hands and feet may be all it takes to locate your beloved diamond ring, especially if it is stuck somewhere in the carpet.
Not Assuming That it Bounced like a Ball
Because of their shapes, diamonds do not bounce or roll in the directions you would normally assume for everyday items. This makes it sensible to stop and think of the least likely places and check there first.