We introduce the concept of mechanochemically gated photoswitching. Mechanical regulation of a photochemical reaction is exemplified using a newly designed mechanophore based on a cyclopentadiene-maleimide Diels-Alder adduct. Ultrasound-induced mechanical activation of the photochemically inert mechanophore in polymers generates a diarylethene photoswitch via a retro-[4 + 2] cycloaddition reaction that photoisomerizes between colorless and colored states upon exposure to UV and visible light. Control experiments demonstrate the thermal stability of the cyclopentadiene-maleimide adduct and confirm the mechanical origin of the "unlocked" photochromic reactivity. This technology holds promise for applications such as lithography and stress-sensing, enabling the mechanical history of polymeric materials to be recorded and read on-demand.