1. A method to determine a state of a media device, the method comprising: processing a first output signal from a first sensor measuring a first property of the media device to generate a first parameter value; processing a second output signal from a second sensor measuring a second property of the media device to generate a second parameter value; generating a first state probability by combining a first conditional probability that the first parameter value corresponds to the media device being in a first state and a second conditional probability that the second parameter value corresponds to the media device being in the first state; generating a second state probability by combining a third conditional probability that the first parameter value corresponds to the media device being in a second state and a fourth conditional probability that the second parameter value corresponds to the media device being in the second state; and determining a detected state of the media device by selecting a greater of the first state probability or the second state probability.