Recent Kaikoura Quake gave 19 seconds warning to a resident of Wellington.
Despite being only a single unit with no link to other warning devices, the unit reacted to the Pwave, giving what turned out to be 19 seconds warning of the shock wave. This enabled him to get his family up and into a safe area where they could duck, cover hold. Initially there was thought it was a fasle alarm as it took so long, but certainly not after it arrived.
Taiwan 5 Seconds
In Tawian, , the recent 6 Feb quake contained a killer pulse that destroyed buildings and while the national system provided warning this takes a few seconds, but the local onsite units provided vital 5 seconds warning, well ahead of the central system.
For more information see:-
Jenlogix and San Lien
Earthquake Warning Systems