The DHS BioWatch program is a federal air-monitoring network operated by the Department of Homeland Security that continuously samples outdoor air in more than 30 major U.S. metropolitan areas for traces of pathogens likely to be used in a biological attack.1Department of Homeland Security. BioWatch Fact Sheet Its job is to buy time. Many of the most dangerous bioweapon agents, anthrax spores in particular, can be treated with antibiotics if caught early but are lethal once symptoms appear. By flagging an invisible release before people get sick, BioWatch is designed to give public health officials the window they need to push medication out to an exposed population.
The system has been running since April 2003 and targets pathogens on the CDC’s Category A and Category B select agent lists, focusing on those most likely to be aerosolized as weapons.2Nuclear Threat Initiative. The Next Generation of Sensor Technology for the BioWatch Program It has never detected an actual attack, and it has drawn steady criticism over both its detection speed and its false-positive record.
How Detection Works
BioWatch relies on fixed outdoor air-sampling collectors placed throughout each participating metropolitan area. The devices draw ambient air through specialized filters that capture airborne particles, including any biological material present.
The rest of the process is manual. Field technicians physically retrieve the exposed filters, typically once every 24 hours, and deliver them to designated laboratories in the Laboratory Response Network. Analysts there use Polymerase Chain Reaction (PCR) testing to look for the DNA or RNA signatures of targeted pathogens. Between collection frequency and lab time, results usually come back 12 to 36 hours after a sample is taken. That delay is the program’s most-criticized limitation, since a fast-moving release can outpace the detection cycle.
During major national events, BioWatch supplements the fixed network with portable sampling units. In 2015 and 2016 alone, the program supported more than 110 national special security events and other high-profile gatherings.3NCBI Bookshelf. Strategies for Effective Improvements to the BioWatch System For those deployments, some sites tighten their collection schedule to every 8 or 12 hours.
Where BioWatch Operates
The network covers more than 30 metro areas chosen for population density and the potential consequences of an attack.4U.S. Government Accountability Office. Information Technology – Federal Agencies Face Challenges in Implementing Initiatives to Improve Public Health Infrastructure The specific cities are not publicly disclosed for security reasons, though congressional testimony has referenced 34 of the largest metro areas as participating jurisdictions.5The Committee on Energy and Commerce. Memorandum – Hearing on BioWatch and Public Health Surveillance
The operating model is federal on paper and local in practice. DHS supplies the detection equipment and sets program direction; state and local public health departments run the daily work, deploying technicians, performing lab analysis, and maintaining response plans. Local jurisdictions absorb real costs for staffing and lab resources on top of the federal investment.
What Happens When Something Is Detected
When a laboratory identifies a potential biological agent in a sample, the finding is classified as a BioWatch Actionable Result, or BAR. That triggers a notification chain built to get decision-makers on the phone quickly.
Within two hours of a confirmed BAR, the local BioWatch Advisory Committee convenes a conference call. The committee draws representatives from public health, emergency management, law enforcement, and environmental health agencies, and the jurisdiction’s local FBI weapons-of-mass-destruction coordinator is looped in early.6NCBI Bookshelf. The BioWatch Program – What Information Is Needed to Inform Decision Making The committee decides on next steps, which can include environmental sampling to confirm the finding, epidemiological surveillance, and public messaging.
If the situation points to a credible large-scale exposure, the response escalates to a BioWatch National Conference Call. From there, participants can reach consensus on requesting the Strategic National Stockpile, the CDC-managed federal reserve of antibiotics, vaccines, and emergency medical supplies. Activation typically requires a federal, state, or local declaration of a public health emergency. The CDC’s Cities Readiness Initiative, launched in 2005, funds state and local health departments specifically to plan for receiving, storing, and dispensing those assets. A confirmed BioWatch detection is considered one of the most realistic scenarios in which the Stockpile would actually be deployed.7National Academies of Sciences, Engineering, and Medicine. Appendix E – Invited Paper – BioWatch Program Overview – A Local Public Health Perspective for Enhancing Bioterrorism Preparedness and Response
If a BAR is confirmed as a real event, the FBI serves as the lead federal agency for any criminal investigation.
Legal Authority and Who Runs It
BioWatch doesn’t rest on a single statute. Its foundation is a mix of presidential directives and legislation built up after the 2001 anthrax letter attacks. President George W. Bush announced the program in his January 2003 State of the Union address as a “network of sensors to detect biological attack.”8The National Academies Press. DHS BioWatch Program – Purpose, Scope, and Legal Authority – The BioWatch System The following year, Homeland Security Presidential Directive 10, “Biodefense for the 21st Century,” set the broader policy framework for biological surveillance and detection and explicitly covered BioWatch.
Management has moved around within DHS. The program originally sat in the Office of Health Affairs. The Countering Weapons of Mass Destruction Act of 2018 consolidated chemical, biological, radiological, and nuclear defense work into a new Countering Weapons of Mass Destruction (CWMD) Office, which took over BioWatch.9Office of the Law Revision Counsel. United States Code Title 6 – 591 Countering Weapons of Mass Destruction Office Another shift is on the way: the President’s Budget for fiscal year 2026 proposes transferring BioWatch’s operational programs from CWMD to the Cybersecurity and Infrastructure Security Agency (CISA) Operations and Support account.
Reliability Concerns
Every BioWatch Actionable Result declared since the program began has turned out to be a false positive.10NCBI Bookshelf. Biowatch and Public Health Surveillance – Evaluating Systems for the Early Detection of Biological Threats – Abbreviated Version That record has two readings. No actual bioterrorism attack has occurred against a monitored city, so a run of negatives is expected. At the same time, each false BAR triggers a disruptive and expensive response, and those costs land on state and local budgets that DHS does not reimburse.
A 2015 GAO review found that DHS lacked reliable information about the current system’s actual ability to detect a biological attack. DHS had commissioned performance tests but had never set the specific performance requirements needed to interpret the results. Officials said the system could detect “catastrophic” attacks causing at least 10,000 casualties, but GAO found no comprehensive analysis combining modeling and test data to support the claim.11U.S. Government Accountability Office. Biosurveillance – DHS Should Not Pursue BioWatch Upgrades or Enhancements Until System Capabilities Are Established Because live biological agents cannot be released in real cities, all performance data comes from chamber testing and simulated agents, which caps how much confidence anyone can place in it.
Attempts to Modernize the Technology
The technology fielded in 2003, commonly called Generation 2, still relies entirely on the manual collect-and-lab process in use today. DHS spent years pursuing a next-generation system, Generation 3, that aimed for autonomous on-site detection with a roughly six-hour turnaround. That effort stalled amid cost overruns and technical concerns, and GAO recommended against further upgrades until DHS set baseline performance requirements for the existing system.
A later modernization effort, Biological Detection for the 21st Century (BD21), tried to broaden the detectable threat range and integrate automated detection. BD21 was discontinued in 2024 after a technology readiness assessment found that the critical technologies it required did not yet exist. DHS issued a final discontinuation report on September 30, 2024, and closed out all BD21 activities.12U.S. Government Accountability Office. Biodefense – DHS Exploring New Methods to Replace BioWatch The program’s annual federal budget was approximately $87 million in FY2025. Operational responsibility is slated to move to CISA under the FY2026 budget proposal, but the manual Generation 2 technology remains the backbone of the system with no announced replacement on the horizon.