You can also use other gestures, like slide up from the bottom or slide down from top of the screen while its off, and have it perform a different action like, unlock the device or launch a particular application. Right from your locked device with the screen being off!
SmartTap uses the digitizer sensor when the screen goes off, without keeping the screen on. Battery consumption is said to be minimal; however, a flipswitch lets you turn the tweak on or off at any time.
You can purchase SmartTap from the Cydia Store for $1.99.