Uploaded October 2020 | Updated September 2026, 1 week ago

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Vintage photo switch unit made in the 1930's or 1940's by Photoswitch Incorporated Cambridge Massachusetts. Operates by using a light beam to illuminate a Photocell and when the beam is interrupted the Photocell triggers an electrical relay via 25L6 Tetrode vacuum tubes. May have been used as an early style intruder alarm or shop door sensor.