1. A system comprising: a logging device including: a magnetometer designed to be in close proximity to a small magnet in an eye patch, the magnetometer to monitor a magnetic field, generated by the small magnet, earth, and proximate magnetic devices; a memory to store data from the magnetometer; and a communication link to obtain the data from the memory, the data processed to show a pattern of wearing and not-wearing the eye patch, to monitor compliance with a medical prescription.