No IP address, no WiFi, works in a power failure, warns workers and drivers with a loud (124 db) signal:

  SonoBlaster(R) Work Zone Intrusion Alarm – SonoBlaster® is an impact-activated safety device that warns work crews and errant vehicle drivers simultaneously to help prevent crashes and injuries in work zones. The NCHRP 350 accepted SonoBlaster® mounts on typical work zone barricades, cones, drums, delineators, A-frames and other barriers. Upon impact of an errant vehicle, the SonoBlaster’s built-in CO2 powered horn blasts at 125 dB to signal workers that their protective zone has been violated, giving them critical reaction time to move out of harms way.

From the webpage of the manufacturer, Transpo Industries.