A device for determining the filling level of a fluid in a container, in particular in the oil reservoir of a vehicle, is provided. The device has at least one sensor element, at least one control unit, at least one energy source, and at least one transmitting unit for wireless transmission of measured data. The at least one energy source is a thermal generator, in particular a thermocouple. The device has at least one energy storage device. The thermal generator is configured for measuring a time-dependent temperature gradient, the thermal generator has a signal-conducting connection to the control unit, and the control unit is configured for placing the device from an energy-saving state into a ready-to-measure state. A method for determining the filling level of a fluid in a container using the device, and a vehicle with the device, in particular a motor vehicle, are also provided.

An oil drain plug and wireless oil level sensor assembly is provided including an oil drain plug having a shaft and a head, the shaft having external threads and an axial passage extending axially therein in communication with at least one radial passage extending through the shaft from the axial passage to an exterior of the shaft. An oil level sensor includes a housing having an annular mounting portion defining an aperture extending there through for receiving the shaft of the oil drain plug. A pressure transducer is in fluid communication with the aperture and connected to a circuit and a battery disposed within the housing that provide wireless signals representative of the oil level.