Detection dogs

No Trace Project > Threat Library > Techniques > Detection dogs

Detection dogs are dogs trained and used by an adversary to detect odors. Detection dogs can be used to detect substances such as explosives or drugs, track people, and participate in scent lineups to determine if a person's scent is present on an item.

An odor is caused by volatile chemical compounds emitted by a substance. For example, the odor of an old book is caused by chemical compounds released into the air by its pages, which are constantly decomposing.

Human scent, the odor of a human body, is caused by chemical compounds emitted by water secretions (sweat), oil secretions (sebum), skin flakes, and body openings (mouth, nose, etc.) Each person has a relatively unique scent that is relatively stable over time.

The sense of smell of dogs is much more complex and developed than that of humans. Dogs can:

• Detect very faint odors.
• Detect a single odor in a mixture of odors.
• Identify the direction from which an odor is coming.
• Perceive the intensity of odors with great precision. This can allow them, for example, if two odors were left in similar conditions, to determine which of the two odors is the most intense, and therefore the most recent.

An adversary can train detection dogs to detect the odors emitted by substances such as explosives, drugs, fire accelerants, or, less commonly, electronic devices. The adversary can use detection dogs:

• At an action site or during a house raid or covert house visit to determine if a substance is present and locate it.
• During an ID check to determine if the person being checked is carrying or has been in contact with a substance.

In many countries, the State uses detection dogs to detect illegal substances at borders, airports, train stations, etc.

When a person moves on foot, they leave behind an odor trail composed of:

• Their scent, including the odors emitted by water (sweat) and oil (sebum) secretions of their feet and by skin flakes falling from their body. Odors from sweat and sebum penetrate shoes, including rubber shoes.
• Odors of things stuck to the soles of their feet or shoes.
• If they wear clothes: odors of particles detaching from their clothes.
• If they wear shoes: odors of the materials the shoes are made of (rubber, leather, etc.)
• If they step on and break living plants, including grass: odors of sap released by broken plants and odors of bacteria breaking down dead parts of plants.
• If they step on and kill insects or other small animals: odors of the dead animals.

An adversary can train detection dogs to follow such an odor trail. There are two tracking methods:

• First method: The dog is provided with an odor, for example in the form of an item of clothing worn by a suspect, and is asked to locate and follow a trail that contains the odor. This method is more reliable.
• Second method: The dog is asked to locate and follow a trail without being provided with an odor. This method is less reliable.

In many countries, the State uses detection dogs to track suspects, but because dogs are not considered reliable, the result of the tracking is not considered strong evidence in court. In some countries, the result of tracking by the first method is considered strong evidence, but the result of tracking by the second method is not.

Detection dogs can often follow an odor trail up to two or three days after it was left, or even, depending on various factors, up to two or three months. Factors that affect the ability of a detection dog to follow a trail a long time after it was left include:

• The training of the dog and of its handler.
• Human activity on or near the trail.
• Wind. Air movement can displace the volatile chemical compounds that constitute a trail.
• Precipitations. Rain, snow or dew can dissolve some of the volatile chemical compounds that constitute a trail.

An adversary can train detection dogs to participate in scent lineups. To set up a scent lineup, the adversary collects scent samples from a suspect and a few other people, typically between 5 and 10, and places the samples next to each other, typically in an empty room with some distance between two samples. The adversary then provides the dog with an odor and the dog is asked to determine which of the scent samples, if any, matches the odor. Typically, the dog is provided with an item collected at an action site that is suspected of carrying the suspect's scent: if the dog determines that the suspect's scent sample matches the item's odor, the adversary can conclude that the suspect was in contact with the item and may have participated in the action.

In countries where the State uses scent lineups, the result of a scent lineup is often not considered strong evidence in court.

Used in tactics: Arrest, Incrimination

Mitigations

Name	Description
Careful action planning	An adversary can use detection dogs to track you after an action. To mitigate this, when leaving the action site, you can plan to: Avoid leaving behind an item that carries your scent, which the adversary could provide to a dog to help the dog track you. Break your odor trail, for example by travelling a significant distance on a bike or crossing a large body of water.

Used in repressive operations

Name	Description
Repression against Zündlumpen	In some of the February 2025 raids, police used detection dogs to locate electronic devices.[1]
Bure criminal association case	Detection dogs were used in one of the raids.[2]
Fenix	In one of the house raids, the police used detection dogs trained to detect explosives.[3]