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; combining first conditional probabilities of the first parameter value and the second parameter value to determine a first state probability for the first state of the media device, wherein the first conditional probabilities are representative of probabilities the first parameter value corresponds to the media device being in a first state; combining second conditional probabilities of the first parameter value and the second parameter value to determine a second state probability for the second state of the media device, wherein the second parameter conditional probabilities are representative of probabilities second parameter value corresponds to the media device being in a second state; and determining a state of the media device by selecting the greater of the first state probability or the second state probability.