Intrepid XDA-Developers users found ways to make the Xperia Z1 work with passive styluses, similarly to the Z Ultra, and to activate the dormant double-tap to wake feature of the Xperia Z, ZR, and ZL (AOKP only).
Starting with the pen mode, XDA user RyokoN came up with a method to activate the Xperia Z1 screen’s hidden ability to work with just about any pen or pencil, just like the Xperia Z Ultra. For some reason, the feature was disabled on Sony’s latest flagship, but RyokoN worked around the limitation starting from similar code in AOKP. RyokoN’s mod works with the stock ROM, you just need to be rooted.
To activate the pen mode on the Xperia Z, you just have to add two lines to a configuration file on the phone. Even better, RyokoN kindly made an app to help you out, that you can check out on this thread. After you run, you should be able to doodle and write on your 5-inch Xperia Z1 to your heart’s liking, though obviously you won’t enjoy any of the features made possible by an active stylus.
The second mod also involves AOKP, but to enjoy it, you will need to run the custom ROM on your Xperia Z, Xperia ZR, or Xperia ZL. A recently merged kernel patch enables the ability to wake up your device simply by tapping on the screen twice. This feature was first introduced on the Xperia Tablet Z, while LG users may be familiar with it from the LG G2 and G Pro 2. According to the developer that enabled the feature, the required drivers were present in the original firmware, but they were locked. The mod simply unlocks them, and, because this is a hardware-level function, battery life shouldn’t be affected significantly.