1. A device comprising: a sensor comprising a light emitter and a light detector configured to generate signal samples, wherein each signal sample includes a first signal generated when the light emitter is on and a second signal generated when the light emitter is off; and processing circuitry coupled to the sensor capable of: performing one or more variance calculations for each signal sample, the one or more variance calculations for each signal sample indicative of a first condition or a second condition; in accordance with a threshold number of signal samples within a threshold period of time indicating the first condition, determining that the device is not secured to an object; and in accordance with fewer than the threshold number of signal samples within the threshold period of time indicating the first condition, determining that the device is secured to the object.