OpenEEW - earthquake early warning by everyone?
In fact it is possible, the early warning system is not something more than a series of accelerometers (seismometers). There is always an epicenter for an earthquake. closer sensors to the epicenter shorten the time for occurrence announcement and more time for far locations to get ready.
There are even some efforts to use personal cellphones accelerometer sensors as a part of broad early warning system. for example here and here . RaspberryShake home sensors can also contribute in a global effort to shorten seismic events announcements. you can follow some live data shared by this home instruments in Iris jamaseis software, freely.
This should be noted that all these efforts are still in early stages. Currently some seismically active cities are equipped with early warning systems but not based on home sensors but on seismic networks.