A guide for public safety What is through wall sensing?

1. The short answer

Through wall sensing tells a team whether a person is in a room they cannot see into. It gives that answer before anyone opens the door. It answers one narrow question room by room. Is someone there and how sure is that answer?

It is not a camera and not a window into the room. It shows no picture of the space or the people in it. A good system reports a few plain answers for each room. It puts a confidence on every answer and says so openly when it cannot tell.

2. The five answers

The useful output is short. On Vantage every room comes back with up to five answers. The through wall detection capabilities page covers each one in full.

• Presence. Is anyone there? Each room reads as occupied, clear or honestly unknown. It keeps updating while the team works.
• Movement. Moving or still for every person found. Someone heading for an exit needs different help from someone who has not moved in minutes.
• Breathing when conditions allow. A person who cannot move is not an empty room. A breathing rate is shown for a still person only when the read is confident.
• Count. How many people are in each room. When the number cannot be pinned down it is given as a range instead of a guess.
• Confidence. How sure each answer is. Every reading carries a score so a crew can tell a strong read from a weak one.

3. The four room states

Those answers roll up into a state for each room. Four states cover every case and each one points to a next step.

Why a no read is never a clear

A no read means the system could not see into the room. It says nothing about whether the room is empty. Being wrong costs far more in one direction than the other. A false clear sends a crew past a room with someone in it. A no read only means that room is searched by hand.

So weak evidence should push a room toward low confidence or no read and never toward clear. Vantage is tuned to report no read long before it would risk a false clear. A room it cannot read stays on the search plan. The guide to presence of life detection goes deeper on reading confidence.

4. How it differs from cameras and thermal imaging

Responders already carry tools that help them see. The difference is in what the operator gets back.

Imaging tools give the operator a picture to interpret. Vantage gives an answer instead and deliberately stops there. It produces no images and records no audio. It never identifies anyone. That keeps the output on the decision in front of the team. It also keeps the inside of a home from being captured in detail.

Through wall sensing does not replace a thermal camera once a crew is inside. The two answer different questions at different moments. One works before the door and the other works in the room.

5. Who uses it

• Fire and rescue. Primary search at structure fires and voids after a partial collapse. Interior rooms after a storm and welfare checks behind a locked door. See through wall sensing for search and rescue and the search and rescue guide.
• Law enforcement. Barricades and hostage response. High risk warrants and finding a downed officer or victim. Always under a recorded lawful basis. See through wall sensing for law enforcement.
• Facility teams. Emergency planning and response inside buildings an organization owns or runs. Never to monitor employees or guests. See facility protection.

6. The legal basis

This section covers the law in the United States. Other countries set their own rules. Under the Fourth Amendment the home is the most protected place in the law and through wall sensing sits squarely inside that protection.

Kyllo v. United States (2001) is the key decision. The Supreme Court held that using a device not in general public use to learn details inside a home is a search when those details could not otherwise be learned without going in. Without a warrant that search is presumptively unreasonable.

Brigham City v. Stuart (2006) sets out the emergency exception. Officers may enter a home without a warrant when they have an objectively reasonable basis to believe someone inside is seriously injured or about to be.

In practice a session needs a lawful basis before anything is read. Vantage requires one of four bases and records it before a session opens.

• Warrant. Bound to the court and case number along with the address and time window.
• Consent. In writing from a person with authority over the premises.
• Emergency. For an imminent threat to life. The incident commander is named and a supervisor is notified immediately.
• Training. On your own facilities with people who have agreed to take part.

A named supervisor confirms the basis. Every session ends in a sealed record that cannot be edited. The through wall sensing governance model explains each control. Whether a basis is lawful in a given case is for your agency and its counsel to decide and for the courts to review. This guide is not legal advice.

7. Limits

Every through wall system has limits. The honest ones show them inside the reading itself. These are the conditions that lower confidence most often.

• Dense concrete, steel and deep debris. Readings cannot form. Those rooms return no read and are searched by hand.
• Many people in one room. Individual counts blur together so the count becomes a range.
• A still and silent person. Breathing needs time and calm conditions to confirm.
• Heavy movement nearby. Machinery, fans, moving water and other crews lower confidence.
• Animals. Large animals can read as occupants.
• Below grade and flooded spaces. Basements and flooded rooms may not resolve.

The full list with what to do in each case is on the limits of through wall sensing page.

8. Questions to ask about any through wall system

These questions separate a useful tool from a risky one. Ask them of Vantage and of anything else you evaluate.

1. Does every reading carry a confidence room by room?
2. What does the operator see when a room cannot be read? Can an unknown room ever show as clear?
3. Will you test it in our buildings against ground truth our team controls? Will you report every miss?
4. Does it produce images or record audio? Does it try to identify anyone?
5. What basis must be recorded before a session opens? Who confirms it?
6. What record does a session leave? Can anyone edit it afterward?

Vantage answers each of these in writing. Every pilot program ends with the misses on the table.

9. Public sources

The descriptions below are our own short summaries. Read the originals for the full picture.

• Detection of Presence of Life (DePLife) Prototype Operational Field Assessment Report. DHS Science and Technology Directorate (2023). Police officers and firefighters tested a prototype in the field for finding people behind walls. They found it quick to set up. They also said missed detections and false alarms lowered their trust in its results. The report covers a different product. We cite it for what responders said they need.
• Through-the-Wall Sensors for Law Enforcement: Market Survey. National Institute of Justice (2012). NCJ 240729. An early federal survey written to help agencies weigh what these tools can and cannot do. It names firefighting, collapse rescue and tactical operations as the main uses. The market has changed a great deal since.
• Kyllo v. United States, 533 U.S. 27 (2001). The Supreme Court decision on using technology to learn what is inside a home.
• Brigham City v. Stuart, 547 U.S. 398 (2006). The decision on entering a home without a warrant to help someone seriously injured or in danger.