[v1k1nG]

Check if player is in a vehicle.
https://sampwiki.blast.hk/wiki/IsPlayerInAnyVehicle

Check which vehicle is the player driving.
https://sampwiki.blast.hk/wiki/GetVehicleModel or https://sampwiki.blast.hk/wiki/GetPlayerVehicleID

Check if the player driving the hydra is in the area.
https://sampwiki.blast.hk/wiki/Areacheck

Send him the message.