An optical trackpad is an input device

Input device

In computing, an input device is any peripheral used to provide data and control signals to an information processing system such as a computer or other information appliance...

 based on an optical sensor, which detects the displacement of a finger that is moving on top of it. It made by CrucialTec CO.,LTD. It's well known by RIM Blackberry series (Bold 9700, curve 8500 series, torch 9800, android smartphones like HTC Desire

HTC Desire

The HTC Desire is a smartphone developed by the HTC Corporation, announced on 16 February 2010 and released in Europe and Australia in the second quarter of the same year. The HTC Desire runs the Android operating system, version 2.2 "Froyo"...

, other feature phones like Samsung mobile Ch@t322..) The sensor is used typically in smartphone

Smartphone

A smartphone is a high-end mobile phone built on a mobile computing platform, with more advanced computing ability and connectivity than a contemporary feature phone. The first smartphones were devices that mainly combined the functions of a personal digital assistant and a mobile phone or camera...

s where it replaces the D-pad

D-pad

A D-pad is a flat, usually thumb-operated directional control with one button on each point, found on nearly all modern video game console gamepads, game controllers, on the remote control units of some television and DVD players, and smart phones...

. The main advantages over a D-pad are:

• It can track movements in 360 degrees and with varying speeds.
• It uses space efficiently, without the need for small buttons that are difficult to press.

Next to browsing through menus, it can drive a mouse cursor in point&click interfaces.

In comparison with trackpads, it detects actual skin displacement, instead of displacement of the center of the area being touched.