The device described here offers a low-cost alternative for real-time temperature-based IVR adherence monitoring. The design is based on the widely used 8-bit Microchip PIC12 microcontroller platform. The circuit uses 8 discrete surface-mount components on a single PCB, with a total cost for components, PCB fabrication, and assembly of US$6 in quantities of 5000, including batteries. This is the cost for the device only and does not include IVR manufacture. A number of characteristics and advantages of the PIC12F683 microcontroller are described above. Use of the PIC12 internal comparator and non-volatile memory enabled the IVRs to use only 8 circuit components and achieve the smallest possible PCB size. The PIC12 data memory is limited to 256 bytes and required the use of a novel data reduction scheme to achieve storage of 2048 IVR status values for retrieval following IVR use. Our approach was to compare a measured voltage proportional to IVR temperature to a reference temperature to determine IVR insertion or removal status, but to store the data in bytes containing eight sequential 1-bit representations of OUT (0) or IN (1) instead of actual temperature values. Data files are retrieved from the device in hexadecimal format, and direct conversion to binary values results in a sequence of 0 and 1 values indicating IVR OUT or IN, respectively, at each predetermined logging interval. An important aspect of the device design is the ability to programmatically set the reference temperature through a simple software setting. For the studies described here, a reference temperature of 34.4°C was used. This temperature was selected based on the temporal variation in macaque vaginal temperature described by Boyd et al. and the normal sheep body temperature measured in this study and by others, with a margin for error to prevent false readings of IVR removal. The reference temperature will need to be optimized in clinical trial to accommodate differences between human and sheep basal temperatures.