I didn't know is the Dexcom G4 actually an implant, because it comes out from your skin. Devices like this are pretty common with diabetics nowadays

I was assuming OP was referring to custom-built projects. I too have a CGM (thanks to the recent Australian Federal subsidy) - a massive shame the technology isn't more open.

If using the Dexcom G4, you need to solder one of these to use it with xdrip

https://xdripkit.co.uk/

G5 works directly with the software because the transmitter speaks Bluetooth.