Methods, systems, and apparatus, including computer programs encoded on a computer storage medium, for proximity-based device access. In some implementations, a first electronic device receives, over a wireless communication link, a message from a second electronic device in proximity to the first electronic device. The first electronic device determines that the second electronic device has been previously associated with the first electronic device as an authentication factor for accessing the first electronic device. The first electronic device receives an encrypted form of a password from the second electronic device over the wireless communication link. The first electronic device determines the password from the encrypted form of the password and provides the password to software executing on the first electronic device to enable access to the first electronic device.