A smoke detector includes an illuminator, a light sensor, a memory, and a microprocessor. The illuminator is configured to emit a first electromagnetic signal having a first center wavelength and a second electromagnetic signal having a second center wavelength. The light sensor is configured to generate (a) a first clean-air voltage in response to receiving the first electromagnetic signal and (b) a second clean-air voltage in response to receiving the second electromagnetic signal. The memory stores non-transitory computer-readable instructions. The microprocessor is adapted to execute the instructions to: (i) determine a first signal drift value from the first clean-air voltage and a first reference voltage, (ii) determine a second signal drift value from the second clean-air voltage and a second reference voltage, and (iii) determine the operational state from both the first signal drift value and the second signal drift value.