Are you paranoid about someone using your sleeping face to stealthily unlock your phone? Google can't fix your problem of having privacy-invading housemates, but they can certainly prevent them from sleep-unlocking your phone.
An April security update adds the 'require eyes to be open' optional setting to the Face Unlock menu, which requires you to be awake and have your eyes open to use the face unlocking feature.
No word on how sensitive it is - too sensitive and it may discriminate against habitual squinters out there; not sensitive enough and it may allow open-eye sleepers fly under the radar.
The update also addresses a couple of Bluetooth problems, including dropped audio and a memory leak issue, so you may want to update your phone ASAP even if stealth unlocking isn't an issue for you.