A three-person startup out of Y Combinator's latest cohort recently demonstrated something unsettling: a drone flying through urban corridors, emitting no radio signals, barely a whisper of heat. Traditional radar saw nothing. And yet, Arlo Industries tracked it in three dimensions.
The trick wasn't sophistication. It was silence—or rather, learning to interpret it.
That quiet revolution is reshaping how the world thinks about airspace security. If the last decade of counter-drone defense was dominated by radar towers scanning the sky, the next may belong to distributed networks that listen, watch, and triangulate without ever announcing their presence. It's a shift driven as much by legal constraints and electronic warfare realities as by technology itself. And it's creating openings for companies—some barely beyond the prototype stage—that a few years ago would have seemed laughable next to defense giants like Raytheon or Northrop Grumman.
The urgency is real. Small drones have rewritten the calculus of modern conflict, from Ukraine's fields to the Middle East's contested airspace. The global counter-UAS market, valued at approximately $5.12 billion in 2025 according to one widely cited industry analysis, is projected by some forecasters to approach $28 billion by 2032—though such projections always carry the usual caveats about geopolitical volatility and procurement cycles. What's less debatable is the trend line: defense budgets are shifting toward systems that can detect, track, and neutralize threats measuring less than a meter across, often flying below 500 feet, sometimes costing under $500.
Traditional radar still anchors most installations. Companies like Robin Radar in the Netherlands, France's Thales, and Australia's DroneShield have deployed micro-Doppler and holographic systems at airports and military facilities worldwide. But radar has inherent vulnerabilities. It emits radiofrequency energy that hostile forces can geolocate. It struggles in cities, where buildings create multipath reflections that turn tracking into guesswork. And against very small targets with minimal radar cross-section—especially those flying autonomously, without telemetry chatter—it can simply miss.
So the industry is layering in alternatives. Or in some cases, replacing radar outright.
When Listening Beats Shouting
The technologies cropping up read like a grab bag from different engineering disciplines. Passive RF sensors that triangulate drone control signals without jamming them (important, given U.S. wiretap laws). Acoustic arrays trained to recognize the harmonic signature of quadcopter propellers over urban background noise. Electro-optical cameras running machine vision algorithms. Even cellular networks—those 5G towers blanketing metro areas—are being studied as inadvertent motion detectors, their signals bouncing off moving objects in ways that might, theoretically, reveal an intruder's position.
It's a fundamentally different philosophy. Active systems announce themselves. Passive networks hide and aggregate.
Consider Germany's HENSOLDT, which has fielded its TwInvis passive radar system for years. TwInvis doesn't transmit; instead, it uses FM radio broadcasts and other ambient signals as illuminators, analyzing reflections to detect aircraft. In late 2024, HENSOLDT announced trials with DFS, Germany's air navigation authority, to test the system for civilian air traffic management—a rare crossover between defense tech and commercial aviation safety. Whether it proves operationally viable at scale remains an open question, but the fact that a national aviation regulator is even piloting it signals how seriously passive sensing is being taken beyond the battlefield.
Australia's Silentium Defence delivered its MAVERICK passive radar into the country's Joint Air Battle Management System in July 2024. That integration—linking a non-emitting sensor into a national defense architecture—validated passive radar as more than an experimental curiosity.
On the RF side, Dedrone (acquired by Axon in late 2024) has installed its passive RF-360 sensors at over 800 sites globally, from airports to stadiums. The system geolocates drones by listening to their control links, triangulating position without intercepting communications—a legal nuance that matters enormously in the United States, where non-federal entities face severe restrictions on counter-UAS operations. An interagency advisory from 2020, still the legal baseline, warns that jamming or intercepting drone signals can violate the Wiretap Act and FCC regulations. Detection-only systems sidestep that minefield.
Dedrone's case studies include securing SOF Week in Tampa and supporting Secret Service operations during the 2024 presidential campaign. D-Fend Solutions, an Israeli firm, offers a similar RF-cyber approach; its EnforceAir platform was deployed at the JUNO Awards in Canada earlier this year.
Acoustic detection, long dismissed as niche, is enjoying a modest resurgence. Squarehead Technology's Discovair G2+ uses microphone arrays to localize drones by propeller noise, with European defense customers running evaluations. Germany's Fraunhofer IDMT has announced progress on low-cost acoustic sensors, positioning acoustics as a complement—never a replacement—to RF and optical layers in what the industry calls "fused" architectures.
The Pentagon's Distributed Bet
The U.S. Department of Defense formalized this strategic pivot last year with the establishment of JIATF-401, a joint task force consolidating counter-small UAS efforts across military services. By early 2026, the task force had publicly committed to fielding "low-collateral" interceptors at all U.S. military installations—a goal that places extraordinary demands on the detection layer. Without high-confidence tracking and identification, rules of engagement in civilian airspace become legally and politically untenable.
The procurement environment now favors sensors that deliver precision without the vulnerabilities of active transmission. The Defense Innovation Unit ran a Low-Cost Sensing challenge in 2025, explicitly seeking scalable, affordable systems with cost-of-ownership savings of 50 to 80 percent compared to legacy radar. MatrixSpace won in December, but the challenge itself telegraphed something larger: the Pentagon is betting on networks of inexpensive nodes rather than a handful of exquisite radar installations.
National Defense Magazine reported last summer that the sixth industry demonstration emphasized operation in "dense, contested electromagnetic environments." Translation: systems that emit can be jammed, spoofed, or targeted. Passive sensors sidestep that vulnerability entirely.
Three forces are converging. Operational necessity, learned painfully in Ukraine, where distributed swarms of cheap drones evade single-point defenses. Regulatory constraints, which make passive detection the only legally viable option for most non-federal operators in the U.S. And, perhaps most intriguingly, emerging standards.
The 3GPP—the body that standardizes cellular protocols—finalized Release 19 in 2024–2025, including initial study items on something called Integrated Sensing and Communication, or ISAC. The European Telecommunications Standards Institute followed with a use-case report in early 2025, explicitly listing drone detection among potential applications.
The concept is elegant, if unproven at scale. 5G base stations already flood urban areas with RF energy. By analyzing reflections and Doppler shifts in those signals, the network itself could theoretically detect and localize moving objects without deploying dedicated sensors. Ericsson and other vendors have floated pilot timelines around 2026–2028, with normative specifications possibly arriving in subsequent releases. If it works—and that's a significant if—telcos could find themselves accidental players in national defense.
The YC Upstart and the Old Guard
Which brings us back to Arlo Industries, the three-person team from Y Combinator's Spring 2026 batch. Founder Deo Arlo studied mechanical engineering at Technion and did robotics research before pivoting to defense tech—a background informed by firsthand exposure to drone and missile threats. The company is building "Mentat," a distributed passive mesh network that tracks aerial objects in 3D. According to its pitch, accuracy improves exponentially as nodes are added, addressing a specific gap: low-altitude, RF-silent targets in cluttered terrain where radar underperforms.
Arlo has run field demonstrations and established partnerships in the U.S., Finland, and Estonia. The company's framing is blunt: "Drone detection is our wedge, not our ceiling—the innovation is the network."
Whether the technology scales beyond battlefield trials is an open question. Distributed mesh networks sound compelling in PowerPoint; delivering sub-meter accuracy in real-world conditions, with nodes that cost hundreds rather than tens of thousands of dollars, is another matter. But the timing favors experimentation. JIATF-401's emphasis on low-collateral interceptors creates demand for exactly the kind of high-fidelity tracking that distributed passive systems promise—and traditional radar often can't deliver.
Arlo isn't alone in the startup tier. But the company's approach aligns with a broader shift: from centralized, emitting systems to distributed, silent observers. And in a market suddenly awash in venture interest and government contracts, that alignment matters. Perhaps more than the founders expected.
What Comes Next
The next several years will likely see passive sensing transition from complementary layer to primary architecture in certain scenarios—urban environments, critical infrastructure, major events where the cost of a false positive is measured in lawsuits and headlines, not just operational failure.
Several catalysts loom. ISAC standardization could move from study items to normative specifications, enabling joint defense-telecom pilots around airports, ports, and military bases where cellular coverage is dense and repurposing existing infrastructure minimizes cost. Major events—FIFA World Cup 2026, Olympics 2028—will require airspace security at scale, and non-federal operators can't legally jam or kinetically engage. Expect layered deployments of passive RF, electro-optical, and acoustic sensors feeding fused common operating pictures. These events become proving grounds for enterprise platforms later sold to corporations, universities, municipal governments.
Procurement centralization under JIATF-401 favors modular, standards-compliant sensors. Vendors offering plug-and-play passive systems that integrate into joint architectures—regardless of whether the backend is Anduril's Lattice, a government C2 system, or something else—will have an edge in down-selects.
Challenges remain, of course. Urban multipath still degrades passive radar. RF-silent drones running waypoint navigation evade RF sensors entirely. Acoustic detection struggles with wind and ambient noise. No single modality is a silver bullet, which is why fusion—combining RF, acoustic, optical, and potentially cellular ISAC—will be table stakes. The winners won't be the companies with the best single sensor. They'll be those that orchestrate multiple silent observers into a coherent, actionable picture.
For founders, the opportunity lies in solving the integration problem: low-cost nodes, resilient mesh topologies, edge processing to reduce backhaul, AI that fuses noisy, heterogeneous inputs into tracks that an operator—or an automated effector—can trust. For investors, it's recognizing that the next Palantir or Anduril might emerge not from kinetic interceptors, but from the invisible infrastructure that decides what to shoot.
And for procurement officers navigating budget pressures and evolving threats, it's understanding that the radar era isn't ending. It's just sharing the stage with technologies that listen, watch, and wait. Silent sentinels in a world where the threat, increasingly, no longer bothers to announce itself.
