Medtronic Diabetes -- Guardian Real-Time A stand-alone CGM. Alarms alert user up to 30 minutes before glucose hits upper or lower limit, when glucose is rising or falling rapidly, and when glucose reaches preset high and low values. (A pediatric model, with low-glucose safety alarm, is available for children and teens.) Sensor and transmitter are waterproof for up to 8 feet deep for 30 minutes. Approved for pediatric and adult use.