Did you know it's possible to unlock your Nexus 5 bootloader without wiping user data? If your device has already been rooted and relocked for optimal security, then unlocking is just a button tap away thanks to the latest update to BootUnlocker. Support for Google's latest flagship phone was just added with an update to version 1.4 of the app from XDA member segv11. Sadly, both generations of the Nexus 7 from ASUS remain unsupported.
If you haven't heard about BootUnlocker, it's a simple utility app with a single purpose: toggling the locked state of the bootloader on supported Nexus devices. With the exception of the ASUS-built Nexus 7 (both 2012 and 2013 models), all recent Nexus devices (Galaxy Nexus and newer) have kept their lock state stored in a single memory location on the param (or misc) partition. By flipping that bit directly instead of using fastboot, your data will not be lost. Of course, this partition is normally write protected, thus the requirement that you already have root. By securing other avenues as thoroughly as possible, including a strong password on your lockscreen, you can enjoy the benefits of frequent modding while still ensuring nobody can mess with your device without wiping its data.
Yesterday's update to version 1.4 brings the welcome addition of Nexus 5 support. This brings the family of supported devices to 4, which includes the Galaxy Nexus, Nexus 10, Nexus 4, and now the Nexus 5. Of course, with each new update to the bootloader, it's possible for the memory location for the lock bit to be relocated, but this has yet to happen. Unfortunately, the bootloaders on the ASUS-made Nexus tablets use a more complicated mechanism to manage lock state. While it's possible to work around this, it requires recording individual locked and unlocked states for each device, a feature the developer isn't planning to add.
If you fall into the cross section of people that is both security conscious and eager to flash mods and ROM updates regularly, then BootUnlocker is probably just what you're looking for. It's both open source and free in the Play Store.