The biggest source of interference in your evidence comes from the outside world. Unfortunately, this is also the hardest thing to protect against. External influences can be anything from the wind rattling around the property to passing pedestrians, traffic, trains, aircraft, and even the local wildlife.

All these things can introduce unexplained sounds into your investigation, but there's also the risk of light in the form of car headlights or the sun striking objects in the property at odd angles and causing reflections. The smell of car fumes, cigarette smoke, local farms, or flowers could also drift in through an open window or ventilation.

In rare cases, earthquakes, tremors, and extreme weather may cause vibrations within a property. Vibration may also be caused by passing traffic (especially heavy plant,) road works, nearby construction sites, and underground services such as metro networks. The sound of neighbors moving around their house, talking, or their...