People have made some crazy body modifications over the years but this may be the only one that actually has a practical use. 

Self-professed biohacker Tim Cannon has become the first human being to have a non-medical computer implanted inside his body. The Circadia 1.0 is about the size of a small smartphone and was implanted in Tim’s forearm without the aid of anesthetic or a licensed doctor. The device is designed to gather biometric data and beam it to a mobile device, making Tim Cannon the first DIY cyborg.