Dead simple DIY QuickCover for the N5
The Nexus 5 (and most phones and tablets, I assume) that have official Active/Quick covers use a magnetic sensor. All you really need is any flip cover (I got mine for $5 at a flea market), a flat craft magnet and a little double sided tape.
The magnetic sensor is in the circle marked 'A' in the pic above, I put the magnet underneath the credit card flap in circle marked 'B'. The simplest way to know the correct placement is to turn on the screen, move the magnet around until the screen turns off, put a little sticky tac on the magnet, close the screen so the magnet sticks to the cover. Done. Just tape it in place. If you don't have a credit card flap just cover the magnet in a little fabric.
Serial Phone Upgrader