A photoelectric sensor detects objects using a light beam. It can sense presence, absence, or distance based on how the light is reflected or interrupted. Through-beam sensors detect when an object breaks a light beam between two separate units. Retro-reflective sensors use a reflector to bounce light back to the sensor and detect interruptions. Diffuse sensors detect light reflected directly from the object. Background suppression types ignore distant objects for more accurate detection. Laser sensors offer high precision for small or distant targets.