A detector designed to record the maximum received signal over a particular time span. However, rather than just detecting the overall maximum, the device does not record single very fast signals but only those that last for a significant length of time; in this way it is similar to a resistor-capacitor circuit with a finite time constant that will not respond to fast pulses. It is used for electromagnetic compatibility testing, where it is employed to detect only those signals that pose a significant long-term probability of causing interference.