Update 14 April 2026: article reviewed; TSCM methodology and legal framework (art. 139f Sr, Wpbr) remain fully current.

A bug sweep — also known as a TSCM inspection (Technical Surveillance Countermeasures) — is a professional inspection in which a location is systematically searched for hidden surveillance equipment. This includes hidden microphones, hidden cameras, GPS trackers and listening devices. This article explains step by step how a professional bug sweep works, what equipment is used and what you receive afterwards.

Step 1: Confidential intake conversation

Before the sweep begins, the TSCM specialist discusses your situation by phone or on-site. Topics covered include:

The reason for the sweep (specific incident, suspicion, or preventive)
The type of location (office, home, hotel room, vehicle)
When you last knew for certain the space was “clean”
Who has had access to the space

Based on this conversation, an assessment of the threat level is made and the most relevant detection methods are selected.

Step 2: Location reconnaissance and TSCM plan

Upon arrival at the location, the specialist visually scans the space. A systematic inspection route is then established: from outside to inside, from low to high, from public to private areas. Each room is fully shielded from external signals where possible.

Step 3: Spectrum analysis

Using a broadband spectrum analyser (range: 10 kHz to 24 GHz), the full radio frequency spectrum of the location is mapped. The specialist searches for:

GSM/4G/5G signals (active transmitters broadcasting live)
Wi-Fi signals (2.4 GHz and 5 GHz cameras)
Bluetooth connections (short-range transmitters)
Analogue FM signals (older listening equipment)
Infrared signals (certain types of hidden cameras)

Anomalous signals are marked and investigated further.

Step 4: Non-Linear Junction Detection (NLJD)

NLJD is the method that also detects switched-off electronic equipment — an essential component of every professional sweep. An NLJD device sends a low-power radio signal into the space. When this signal strikes a semiconductor (the building block of every electronic device), it reflects at a characteristic frequency. This makes even completely switched-off hidden cameras and microphones detectable.

NLJD is systematically applied to: walls, ceilings, fixtures, power sockets, ventilation openings, furniture and objects that have had access to the space.

Step 5: Optical camera lens detection

Using a specialised optical detection system, camera lenses are located via their lens reflection. The detection laser locates even pinhole lenses of 1mm diameter, hidden behind dark glass, dust or fabric. This method also detects cameras that are completely switched off and emit no signal whatsoever.

Step 6: Physical inspection

After the electronic detection steps, a thorough manual inspection follows of all suspect locations:

Power sockets and wall outlets
Smoke detectors and CO detectors
Alarm clocks, clocks and USB chargers
Ventilation openings and air filters
Light fixtures and recessed spotlights
Furniture, paintings and decorative objects
OBD port (in vehicles)
Wheels and wheel arches (in vehicles)

Step 7: Network scan

Where applicable, the specialist scans the wireless network at the location for unknown devices. Wi-Fi cameras are connected to a network — once that network has been mapped, the connected devices become visible.

Step 8: Findings and report

After the inspection is complete, the findings are discussed directly. You receive a written inspection report containing:

Date, location and scope of the inspection
Detection methods and equipment used
Findings (both positive and negative)
If found: type of equipment, location, frequency band, photographic documentation
Recommendations for further steps

This report can be used in police reports, civil proceedings and insurance claims.

What if equipment is found?

When surveillance equipment is actually discovered, SAJ Recherche advises on:

Evidence preservation: The equipment is not touched until its evidentiary value has been secured
Police report: Under Art. 139f of the Dutch Criminal Code (maximum 1 year imprisonment)
Legal steps: In cooperation with Breedijk Advocaten for civil or criminal prosecution
Countermeasures: Advice on how to prevent future placement

How often should you have a bug sweep done?

The frequency depends on your risk profile:

High risk (executives, lawyers, sensitive negotiations): monthly or quarterly
Medium risk (regular business meetings, hotel rooms): per stay or after each external access
Preventive (after renovation, staff change, break-in): one-off inspection

Further reading:

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SAJ Recherche B.V. is a licensed detective agency with POB licence 8779, Ministry of Justice. Justis.nl register. KvK: 96790954.

How does a professional bug sweep work? Step by step explained