When logging is enabled and the appropriate number of wake cycles have been completed to reach the set logging interval, the data logging (green) subroutine is entered. The program sets appropriate Vref for determining IN/OUT status (typically ~35°C) at one comparator input and reads Vth at the other. The output is “1” of Vth > Vref (IN) and “0” if Vth < Vref (OUT). This 1-bit value is stored in the current data byte. When 8 IN/OUT bits are accumulated, the data byte is written to non-volatile EEPROM memory. The built-in PIC12F683 EEPROM size of 256 bytes allows storage of 2048 IN/OUT readings. Additionally, the LED may be flashed to indicate a measurement or other device status. The current implementation uses a short LED flash to indicate power on, a 3 sec LED on to indicate logging started or stopped, and a short flash to indicate a logged data value. More complex LED output enabled for debugging has included a double flash for “IN” measurement and single flash for “OUT” measurement with three flashes indicating a successful data write to EEPROM. The LED functionality may be enabled or disabled programmatically in software. During long-term testing and in vivo evaluation, the LED functionality is minimized to preserve battery life.