Here are electronic tattoo sensors that you can put on to comfortably measure ECG, EMG, EEG, and skin temperature. The Graphene Electronic Tattoo Sensor (GET) is made via a wet transfer, dry patterning method. It has a thickness of 463 ± 30 nm. Its open mesh design makes GET more breathable.
These smart tattoos can stay functional for several days. You can read all about them on ACS.