The Ectoplasmic Frequency Monitor is a small monitoring device connected to the Containment Unit that can detect and monitor frequency patterns of captured ectoplasmic entities.
When Kylie Griffin questioned if the Grundel was still in the Containment Unit, the Ghostbusters checked the Ectoplasmic Frequency Monitor. Egon Spengler presented a read out of the Grundel's frequency pattern. The monitor was later used in conjunction with the Ectoplasmic Entity Projection Unit to project the Grundel out of the unit in a containment field so Kylie could learn what happened to her friend Jack.
- On page two of Ghostbusters Volume 2 Issue #3, the Ectoplasmic Frequency Monitor makes a non-canon cameo on top of the side cabinet.