What actually happens during a professional sweep.

We talk first — and not from the room you are worried about, and not on a telephone you suspect. We will happily arrange to meet you somewhere neutral, or speak while you are out of the building.

What we need to understand: what happened that made you call, who has had access and when, what a hostile party would gain, and who inside your organisation knows you are considering a sweep. That last question matters more than any other.

Who is realistically interested, what would they gain, and what could they plausibly deploy? A domestic case and a corporate espionage case call for different searches. A jealous ex-partner buys something off a marketplace. A competitor with real money behind them may field equipment that only transmits for a few milliseconds at a time.

Out of that comes the scope: which rooms, which vehicles, which telephone and data lines, which devices, on what date, and at what hour. We agree it in writing before we arrive, so nobody is surprised by either the invoice or the coverage.

We arrive in plain vehicles and plain clothes. No livery, no branded cases in the lobby, no announcement. If a cover story helps — IT contractors, an air-quality survey, an insurance inspection — we will agree one with you in advance and stick to it.

Before we touch anything we photograph the space. Every item we move goes back precisely where it was. When we leave, the room looks untouched, because the wrong person noticing that a sweep happened is itself a leak.

We establish what the radio environment in your building normally looks like — Wi-Fi, cellular, two-way radio, wireless microphones, the building's own systems, the broadcast towers outside. Without that baseline every reading is meaningless, because a busy office is full of perfectly legitimate signals.

Then we look for what does not belong. A spectrum analyser sweeps from the low kilohertz up into the gigahertz range and shows every carrier present. Anything unexplained gets demodulated and listened to, and correlated against sound we generate in the room.

A great many devices never touch the airwaves at all. They ride the cabling that is already in the building: telephone pairs, network runs, alarm and intercom loops, and the mains wiring itself.

We test telephone instruments and their lines for hook-switch bypass (which turns a handset on the cradle into a live microphone), for series and parallel taps, and for voltage and current that does not match a clean pair. We use a time-domain reflectometer to find physical anomalies along a cable run — an unexpected junction eighty feet down a wall reads on the trace as plainly as a knot in a rope. We examine the AC wiring at very low frequency for carrier-current devices, which use your own mains as their aerial.

This is the longest part, the least glamorous, and the part that finds the devices nothing else can. A recorder that stores to a card emits nothing. A transmitter that is switched off emits nothing. Neither will ever appear on a spectrum analyser — they have to be found by hand.

A non-linear junction detector solves the hard half of that. It responds to the semiconductor junctions inside any electronic circuit, powered or not, so it will register a dormant device buried inside a wall, a chair, a book or a light fitting. Infrared and optical examination covers lenses, laser and infrared links. Then we take the room apart carefully and put it back: fittings, vents, voids, furniture, frames, plates and plugs.

If we find nothing, we tell you that clearly and we tell you what 'nothing' covers: which areas, which frequencies, which lines, on which date. An honest negative is a real result, and it is the result most of the time.

If we find something, we do not simply rip it off the wall. What you want from that object depends entirely on what you intend to do next, and that decision is yours to make with your attorney. It can be left in place and fed, documented and removed under chain of custody, or neutralised on the spot. We will explain the trade-offs before anyone touches it.

You receive a written report: areas covered, instruments used, frequency ranges examined, lines tested, anything recovered, photographs, and our recommendations — including how often this site should realistically be swept again.