Devices having matter differentiation detectors

A device, comprising:

• a first emitter configured to emit a first beam of electromagnetic radiation of a first wavelength, the first wavelength between 750 nanometer (nm) and 1400 nm;
• a second emitter configured to emit a second beam of electromagnetic radiation of a second wavelength, the second wavelength between 1400 nm and 2000 nm, wherein the first beam of electromagnetic radiation and the second beam of electromagnetic radiation have different human tissue reflectance factors, and the first wavelength is different from the second wavelength;
• a photodetector filtered to detect a first notch of the first wavelength and a second notch of the second wavelength;
• a timing circuit configured to operate the first emitter and the second emitter, to respectively emit the first beam of electromagnetic radiation or the second beam of electromagnetic radiation at different times;
• and
• a matter differentiation circuit configured to indicate whether the device is likely proximate to a human tissue, the indication based at least partly on:
• the first notch of the first wavelength detected by the photodetector after the first emitter emits the first beam;
• and
• the second notch of the second wavelength detected by the photodetector after the second emitter emits the second beam.