There are two ways to go about this. The easier route would be to use the spare Dexcom receiver we have - we got upgraded from the original receiver that we had to a receiver with "Share", which enables the Follow app on our phones. I'd use a Pi or something similar to read the data coming from the receiver in realtime over the USB port, and use that to sound local alerts, send text messages, etc.
The other, and perhaps more interesting, approach would be to sniff in on the RF signals coming from the Dexcom transmitter. The transmitter works on the 433 MHz ISM band, and that might make it easy to tap into and make it as seamless as possible for my daughter. I'm envisioning this as a nightstand system, and I want it to "just work" when she lies down to go to sleep. No remembering to plug anything in, nothing to do except be near it and have it work.
Brief Dexcom topology lesson: the G4 CGM system that we have consists of three physical parts:
- A sensor. This is the electrochemical bit that gets injected in her skin and creates a current proportional to the level of glucose in her interstitial fluid. That's replaced every week or so - we usually stretch that out to two weeks or more since they're so expensive;
- A transmitter. This is a little battery powered bit that snaps onto the sensor and drives it, encodes the data, and transmits it as packets on the 433 MHz ISM band; and
- A receiver. Our G4 system - two generations old now - has a separate, dedicated receiver, which turns the data into pretty graphs and sounds alarms when setpoints are exceeded. It also has a Bluetooth connection to her phone, which runs the Share app that lets us see her numbers on the Follow app.