The LG G2 is the first Android smartphone to ship with a unique feature dubbed KnockOn. This feature allows G2 owners to wake up or put the device to sleep by simply double tapping on the screen.
Similar implementations like d2tw (Double Tap 2 wake) or sweep2wake have been seen in the past on various Android devices, thanks to custom kernels. However, these implementations have always been very buggy, rarely worked as intended and had quite a heavy impact on battery life.
The Nexus 5 is the latest handset to get this feature via custom kernels. However, the good news is that this time the kernel developers have actually re-worked the code, making it work flawlessly with lesser wakelocks, leading to a drastic reduction in power consumption. Reports from beta testers of the custom kernels l indicate that there is an additional drain of around 0.5-1% per hour with the feature enabled. While this may sound a lot, especially keeping in mind how poor the Nexus 5 battery life is, the additional drain would be barely noticeable in day-to-day usage.
Right now, only ElementalX, Bricked and Faux123‘s kernel have been updated with the new and updated code. Update for other kernels for the Nexus 5, and even for other Android devices with similar feature, should be coming soon.
I have been using the Bricked kernel with the KnockKnock a.k.a double tap2wake for the last 24 hours and the feature has been working flawlessly. If you have been lusting after the KnockOn feature as seen on the G2, I strongly recommend you to try out one the custom kernels mentioned above.