The Samsung Galaxy Gear has been a big hit with smartwatch fans since its release, but unfortunately hasn't reached a larger set of users due to the small set of devices with which it's compatible. The Galaxy Gear currently only works with Samsung's Galaxy series of phones including the Galaxy Note 3, Galaxy S4, Galaxy S3 and Galaxy Mega. Some hardcore users have taken it upon themselves to get the Galaxy Gear up and running with other devices however, one such method involving the Nexus 5.
If you're a Nexus 5 user and itching to rock a Galaxy Gear, this method does work, though it also takes a decent amount of work to get up and running (and it is a bit messy with scattered APKs). But if you're really looking to use your Galaxy Gear with an "unsupported" device, this is the route to take (for now).
If you managed to do all that correctly you should be able to receive notifications on your watch via the ATN Manager app. They aren't pretty but they do work. Some notifications will show you a message, others only give you the option to view on the phone. Pretty much everything but S-Voice and weather works like a champ — the dialer, voice memo, contacts and find my device. Some work, some don't. Expected when you hack things together :)
We've played around a bit with a few other devices and haven't had much luck using this method, but if you happen to get the Galaxy Gear up and running with another phone, please drop a comment and let us know.