Apple Watch Back Crystal / Sensor Repair at SPR.

• 1The rear glass (the crystal over the sensors on the back) is cracked or chipped — common after dropping the watch back-first or sitting on it.
• 2Heart rate, SpO2 or ECG stopped reading, or readings are wildly wrong — the optical sensor cluster sits right under the back crystal.
• 3The watch keeps saying 'Place your watch on your wrist' even when worn — the back-of-wrist detection sensor is disturbed.
• 4The back glass is lifting or separating from the case — broken adhesive that also breaks the water seal.
• 5Skin irritation or a sharp edge from a cracked back crystal pressing on your wrist.

Workshop-level, typically 2–4 hours. The back crystal is the sapphire or ceramic window over the heart-rate, SpO2 and ECG sensor cluster, bonded to the case with strong adhesive that also forms part of the water seal. We carefully lift the cracked crystal, inspect and where necessary replace the optical sensor array beneath it, then re-seal with fresh adhesive and pressure-test where possible. If only the crystal cracked and the sensors are intact, it's a crystal-and-reseal job; if the impact also damaged the sensor cluster, we replace that too — we tell you which after opening it. Because the sensors are calibrated to the watch, we check heart rate, blood oxygen and wrist detection before returning it. Honest note: a cracked back crystal breaks the water resistance immediately, so even if the watch still works, water and sweat are now reaching the sensors — worth fixing before that corrodes them.