The Radar is a technological device used by Mama's and Sisters, possibly created by the "Demons". The radar can locate and show where people are through the transmitters even at long distances. However, the radar can not identify who the people are.
In general, the radar resembles a watch, being in a circular form with a cover, which protects the glass part of the radar. On every radar, there are marked designs, which indicates where the transmitter holder is, as quoted by Sister Krone.
Three named people have been seen using the device through out the series: