Several measurable changes in the local environment will often accompany less measurable signs of paranormal activity. When these are recorded, they are taken as hard evidence of paranormal activity. Often, fluctuations will occur around a place of interest- for example, a haunt believe to be a dead relative may cause readings near their favorite chair, or a portrait of them.
- Temperature: Areas where a ghost or apparition appears to be may show a significant temperature difference than the surround room, and are known as "hot spots" or "cold spots" accordingly. While these may be felt, a more measurable reading can come from thermometer recordings. Heat-sensitive video recordings can show a shape to these areas; usually they appear as a blob, though the SciFi channel show Ghost Hunters once recorded a thermal image with a human form.
- Radiation: Similar to the spots of temperature differences, electromagnetic radiation detectors may show fluctuations in magnetic fields. Similarly, small amounts of radioactivity may appear. Setting these aside from typical environmental fluctuations is the tendency to occur in one place (especially a place of special meaning), where there is no apparent outside cause. EM radiation is particularly susceptible to false positives from electrical wiring.
- Electronic interference: Radios, television sets, or other wireless equipment may behave strangely, appearing to be caused by stray signals. Remote control televisions may change channels, or have a change in volume. Video cameras left to record may turn off or experience audio or video static.