# Hearing the Drop: Prison Drone Drops: Detecting the Delivery by Sound

> Drones now deliver drugs, phones and weapons into prisons thousands of times a year. New research shows a microphone can tell the moment the package falls.

- Published: 30 October 2026
- Author: Ghulam Mujtaba, Ph.D. (https://drosonic.com/about.html)
- Publisher: DroSonic OSINT (https://osint.drosonic.com/), the research arm of DroSonic (https://drosonic.com/)
- Topics: Prisons, Acoustic Detection, Counter-UAS
- Confidence: moderate
- Web page: https://osint.drosonic.com/assessments/prison-drone-drops-acoustic-detection.html
- Cite as: Mujtaba, G. (2026, October 30). Hearing the Drop: Prison Drone Drops: Detecting the Delivery by Sound. DroSonic OSINT. https://osint.drosonic.com/assessments/prison-drone-drops-acoustic-detection.html
- Reuse: Text and original diagrams © DroSonic. You may quote this report and share its link with credit to DroSonic OSINT; to republish it in full, reuse our diagrams or use it commercially, contact us first. Photos and third-party figures keep the licences shown in their credits.

## Key questions

**How many drones fly over prisons?**
England and Wales recorded 1,712 prison drone incidents between April 2024 and March 2025, up 43% in a year. Canada's federal prisons reported 1,064 in 2024–25, and U.S. federal prisons 479 in 2024, up from 23 in 2018.

**Can a drone detector tell when a drone drops a package?**
Research suggests it can. In a 2026 Université de Sherbrooke study, a ground microphone array detected 96% of test package drops, with false alarms on 8% of moments, by hearing the drone's propeller pitch fall as its 500–600 g load was released. It worked to about 100 m with one drone model.

**Why don't prisons jam or shoot down drones?**
In the U.S., federal law protecting aircraft bars state prisons from shooting down or disabling drones; Georgia's corrections commissioner told lawmakers in December 2025 that they lack the legal authority. Researchers note that local laws often prohibit jamming or interception, which leaves detection and recovery.

## Key numbers

- **1,712** drone incidents at prisons in England and Wales in a year (Apr 2024 – Mar 2025, up 43%)
- **1,064** drone incidents at Canada's federal prisons (2024–25)
- **479** at U.S. federal prisons in 2024 (23 in 2018)
- **96%** of test package drops detected by sound (8% false alarms, one drone, ≤100 m)

## Bottom line

**Prisons in Britain, Canada and the United States now record drone deliveries in the hundreds to thousands a year, and the airspace above some of them has in effect been handed to criminal gangs.** England and Wales logged 1,712 prison drone incidents in a single year to March 2025; Canada's federal system 1,064; U.S. federal prisons 479 in 2024, against 23 in 2018. Most prisons may not jam or shoot down the drones, so their defence is to detect them and recover what they drop before prisoners do. That makes the critical question not *was there a drone?* but *did it drop something, and where?* A February 2026 study from Université de Sherbrooke shows a ground microphone array can answer the first half: it detected 96% of test drops by hearing the drone's propellers slow as the load fell away. The method is young, tested on one drone with a heavy payload, but it points at the gap that radio detectors leave and that prisons most need closed.

## What each sensor tells a prison

| Sensor — at a prison wall | What it tells staff | Where it falls short |
|---|---|---|
| Radio-frequency detector — listens to the control link | That a drone is near; often its make, model and pilot's position | Encrypted links and pre-programmed or autonomous flights give it little to work with |
| Radar — reflected energy | Position and track at range | Costly; small slow drones can be mistaken for birds |
| Camera — visible or thermal | What it is and what it carries | Depends on light, weather and line of sight; deliveries likely cluster at night |
| Microphone array — the rotor's sound | That a drone is near, its direction, and now whether it dropped its load | Short range (about 100 m in tests); noise; one drone model tested so far |
| Networked acoustic nodes — DroSonic's approach | Several cheap passive sensors along a perimeter, each classifying sound on board | Short range per node, so a wall needs many; drop detection not yet shown by DroSonic |

## Five a day, and rising

In England and Wales, the Ministry of Justice reported 1,712 drone incidents at prisons between April 2024 and March 2025, a 43% rise on the previous year, alongside £900,000 for counter-drone work and £40 million already committed that year to netting, reinforced windows and other security. ([GOV.UK](https://www.gov.uk/government/news/counter-drone-efforts-rise-as-prison-sightings-revealed)) In January 2025 the Chief Inspector of Prisons said police and the prison service had "in effect ceded the airspace" above two high-security prisons, Manchester and Long Lartin, to organised crime gangs; at Manchester, prisoners were burning holes in supposedly secure windows to keep receiving drone deliveries. He called the failure "a threat to national security". ([HM Inspectorate of Prisons](https://hmiprisons.justiceinspectorates.gov.uk/news/drones-dropping-drugs-and-weapons-into-high-security-prisons-are-a-threat-to-national-security))

Canada's federal prison service reported 1,064 drone incidents in 2024–25 and 839 in 2025–26. ([CP24](https://www.cp24.com/news/canada/2026/04/21/saskatchewan-to-test-out-technology-that-detects-drones-smuggling-drugs-into-prisons/)) In the United States, federal prisons recorded 479 drone incidents in 2024, up from 23 in 2018, according to Justice Department and FBI testimony. ([Facilities Dive](https://www.facilitiesdive.com/news/prisons-battle-nightly-drone-drops-of-drugs-other-contraband/810430/)) State systems add their own: Georgia's corrections department told lawmakers it had handled nearly 400 drone contraband incidents in 2025 by early December, rising from 17 in January to 63 in each of September and October. ([WSB-TV](https://www.wsbtv.com/news/local/atlanta/corrections-staff-report-nearly-400-drone-incidents-georgia-state-prisons-2025/5AVBQXC4AFEFLPUU7DQJAAHBDQ/))

*Figure: Drones over prisons, as the prisons count them.* Bar chart of drone incidents reported by prison systems: England and Wales 1,712 (April 2024 to March 2025, up 43%); Canada federal 1,064 (2024–25, 839 the year after); United States federal 479 (2024, 23 in 2018); Georgia state prisons about 400 (2025). Each system defines an incident differently; the figures show scale and trend, not comparable rates.

The payloads are not trivial. South Carolina officials described seizing a single drone carrying 464 grams of fentanyl, and phones delivered by drone supported a scam run from a Georgia prison that netted $500,000. ([Facilities Dive](https://www.facilitiesdive.com/news/prisons-battle-nightly-drone-drops-of-drugs-other-contraband/810430/)) Georgia officials also showed lawmakers a confiscated drone able to lift 225 pounds. ([Capitol Beat](https://capitol-beat.org/2025/12/drones-a-threat-to-prison-security/))

## Detect, but do not touch

Most prisons are not allowed to stop the drones. In the U.S., federal law protecting aircraft means state prisons cannot shoot drones down or disable them, even over their own grounds. "We just don't have the authority, the legal authority, to be able to do it," Georgia's corrections commissioner, Tyrone Oliver, told lawmakers in December 2025. ([Capitol Beat](https://capitol-beat.org/2025/12/drones-a-threat-to-prison-security/)) Our report [Allowed to Listen, Not to Shoot](https://osint.drosonic.com/assessments/us-counter-drone-law-detection.html) sets out who may do what under U.S. law.

Britain went the other way on airspace: since January 2024, flying a drone within 400 metres of a closed prison or young offender institution in England and Wales has been an offence carrying fines of up to £2,500, so police no longer need evidence of smuggling before acting. ([DroneLife](https://dronelife.com/2024/01/25/uk-government-implements-no-fly-zones-around-prisons-to-combat-contraband-smuggling-via-drones/)) A no-fly zone still needs a sensor to know when it has been broken.

*Figure: HMP Fosse Way, 2025, the view from above.* Aerial view of HMP Fosse Way, a modern prison of white multi-storey blocks and exercise yards surrounded by fences, trees and housing. A modern prison seen from the air: a compact perimeter with every yard and window block in view.

So prisons fall back on detection and recovery. Detection systems in use are largely radio-based: tracking technology described in RAND research "homes in on the radio signals that all drones release", and vendors say their tracking data can identify a drone's model and owner. ([Facilities Dive](https://www.facilitiesdive.com/news/prisons-battle-nightly-drone-drops-of-drugs-other-contraband/810430/)) The same research expects drone activity to be concentrated overnight, when staffing and perimeter coverage are thinnest. ([Facilities Dive](https://www.facilitiesdive.com/news/prisons-battle-nightly-drone-drops-of-drugs-other-contraband/810430/))

## Knowing it flew is not knowing it dropped

The Sherbrooke researchers frame the problem precisely. Authorities rely on detection systems to identify and track intrusions in real time "and eventually recover packages dropped within the perimeter". Radio eavesdropping can sometimes extract a drone's position and even its delivery state, they note, but encrypted links or an autonomous drone flying a pre-programmed mission make that strategy inefficient. Microphone arrays are cheap and can locate a sound, but have limited range and are sensitive to noise. ([Marcoux & Grondin](https://arxiv.org/abs/2602.09991)) Earlier acoustic research had shown it could tell a loaded drone from an empty one; by the authors' account, nobody had tried to catch the moment of release. ([Marcoux & Grondin](https://arxiv.org/abs/2602.09991)) DroSonic's provisional patent application covers acoustic detection, classification and localisation in general; telling a loaded drone from an empty one is the kind of classification this study shows is possible. ([DroSonic](https://drosonic.com/news/patent-filed.html))

## The pitch of a heavier drone

A drone's propellers each produce a tone at their blade-passing frequency: the number of blades multiplied by how fast the motor turns. A heavier drone must spin its motors faster to hover, so its tone sits higher; when the load falls away, the motors slow and the pitch drops. The Sherbrooke system listens for exactly that. A neural network estimates the blade-passing frequencies of the two loudest propellers from three seconds of sound at a time, and a second algorithm compares the spread of those frequencies before and after each moment, flagging a delivery when the shift is large enough. ([Marcoux & Grondin](https://arxiv.org/abs/2602.09991))

*Figure: Hearing the drop, the pitch falls with the load.* Schematic chart of propeller pitch over time: a higher band while the drone carries 500 to 600 grams, a dashed line marking the package release, then a lower band once the drone is empty. Schematic of the Sherbrooke method. The microphones do not hear the package land; they hear the drone get lighter.

The team flew a modified Holybro X500 V2 quadcopter fitted with a release mechanism and an on-board microphone, and recorded it with a 16-microphone ground array: 28 flights, up to 160 metres from the array, with 23 drops of 500–600 g packages and background recordings of highway traffic, voices and a chainsaw. ([Marcoux & Grondin](https://arxiv.org/abs/2602.09991)) They have published the recordings. ([GitHub](https://github.com/introlab/d3set))

The results: the system recognised whether a drone was present with 97% accuracy and estimated its propeller pitch to within about 16 Hz when it was less than 150 metres away. It flagged 96% of delivery moments while raising false alarms on 8% of moments, and the authors judge it reliable to about 100 metres. It coped well with urban noise, which sits mostly at low frequencies, because a drone's rotors also produce a high-pitched component around 5 kHz. ([Marcoux & Grondin](https://arxiv.org/abs/2602.09991))

## One drone, one heavy load

The authors are candid about what the study does not show:

- **One drone model.** The network was trained on a single quadcopter, so other airframes, motors and propellers may confuse it. Detectors trained on narrow data often lose accuracy on drones, microphones and sites they have not heard before.
- **A heavy payload.** The 500–600 g packages were about half the drone's weight, which made the pitch change large. Lighter drops will shift the pitch less and be missed more often.
- **No position awareness.** The algorithm ignores where the drone is and how it moves, so the Doppler effect, wind gusts or deliberate manoeuvres could trigger false alerts. The authors propose adding direction finding.
- **Small numbers.** The delivery tests come down to 29 test cases. And with the longest analysis window, an alert can lag the drop by up to 7.5 seconds. ([Marcoux & Grondin](https://arxiv.org/abs/2602.09991))

Range is the hard constraint at a real prison. At about 100 metres per array, covering a perimeter means several arrays, placed where deliveries actually happen: over exercise yards, near cell-block windows, along the stretches of wall that cameras cover worst.

### Confidence: How sure we are, and what would change it

**High confidence** in the scale and trend of prison drone incidents, which come from official figures in three countries, though each system counts incidents differently.

**Moderate confidence** that acoustic drop detection can work operationally. The physics is sound and the first results are strong, but they come from one drone, one payload weight and a few dozen events, not a prison.

**What would change it:** a trial at an operating prison with several drone types and realistic payloads, or evidence that lighter drops (a phone, a few grams of drugs) remain detectable.

## Listening along a wall

A prison perimeter suits short-range acoustic sensing: the threat must come close, and the wall is long and fixed. DroSonic's design is a network of small passive nodes, each running its classifier on low-cost edge hardware, so coverage is a matter of spacing rather than one expensive sensor. ([DroSonic](https://drosonic.com/#technology)) Because the nodes only listen, they raise none of the legal questions that jamming does for prisons.

DroSonic has not published results on detecting drops, and this report's evidence comes from one university study. What DroSonic has shown publicly is a prototype tested against live drones at the DIRT Days 26.04 field exercise in September 2026. ([DroSonic](https://drosonic.com/news/dirt-days-field-test.html))

## Listen at the wall

A prison is close to the ideal site for acoustic sensing. The perimeter is short and fixed, the threat comes low and slow to a handful of predictable places, and much of it arrives at night when cameras struggle. Radio detectors hear drones on ordinary radio links well. It is our assessment that smugglers will shift towards the pre-programmed routes and encrypted links that the Sherbrooke researchers say defeat radio eavesdropping, as other drone users already have. A microphone hears a drone whatever its link, and the Sherbrooke work shows it may hear more than presence: it may hear the drop.

At [DroSonic](https://drosonic.com/) we build [passive acoustic detection](https://drosonic.com/#technology) for exactly this kind of short, fixed perimeter. The useful system for a prison is layered: radio detection to identify and locate pilots, acoustic arrays to hear every drone and, increasingly, every drop, and recovery teams sent to the right yard while the package is still on the ground. Our explainer [What a Microphone Can Hear](https://osint.drosonic.com/assessments/acoustic-drone-detection-explained.html) covers what acoustic sensing can and cannot do.

## Related reports

- [Allowed to Listen, Not to Shoot: U.S. Counter-Drone Law: Who May Detect](https://osint.drosonic.com/assessments/us-counter-drone-law-detection.html): The SAFER SKIES Act gives U.S. police counter-drone powers. Stopping drones stays with certified agencies; how you detect one still matters.
- [What a Microphone Can Hear: Acoustic Drone Detection Explained](https://osint.drosonic.com/assessments/acoustic-drone-detection-explained.html): Acoustic sensors detect drones by the sound they can't switch off. How they work, how far they hear, and where they beat radar and RF.
- [Listening to the Sky: Acoustic Drone Detection: WW1 to Sky Fortress](https://osint.drosonic.com/assessments/listening-to-the-sky.html): Ukraine rebuilt a century-old idea, listening for aircraft, with thousands of cheap microphones. How it works, where it fails, and how the U.S. could use it.