Oil Tank Monitor UK

Hi can anyone recommend a suitable oil tank monitor that works with Smart Things

  • the tank is 30 yards away from the hub but line of sight through 3 thick stone walls and the tank is made of cast iron (yes!! local planning regulation)

I had thought about this before and had a simple plan of using a float switch contacts switch a relay and monitor the relay for a change of state indicating low level ,… or go mad and use existing ultrasonic devices available to switch a fibaro smart implant for example…