Trades, plant operators and the site office on one channel, on whatever hardware the site already issues — including rugged handsets with a real push-to-talk key.
The ring thickens with your voice, so an operator can see the mic is picking them up over the plant without taking their ear defenders off to check.
A subcontractor can be added to the one channel they need for the weeks they are on site, and removed the day they leave.
Emergency on push.tt is a state, not a chime. It persists until somebody clears it, and it overrides Do Not Disturb, Busy and channel mute.