Do fitness trackers still work if you have tattoos?

The honest answer is: maybe, and Engadget actually breaks down why — the optical heart rate sensors that most wearables rely on can struggle with the ink pigments and density of tattoos, with darker and denser ink causing the most interference. This is genuinely useful information if you're tattooed and shopping for a fitness tracker or smartwatch, since no manufacturer is going to put 'may not work on your wrist' in the marketing copy. Worth a read before you commit to any wrist-worn health device.