Concept renderGPS spoofing feeds a receiver fake satellite signals so it reports a false position or time. Jamming drowns the real signals in noise. A small tracker can flag both by reading receiver jamming and spoofing states, gain and signal strength, position jumps, and disagreement with cell or Wi-Fi location. No flag can prove a position is genuine.
Fleet, pet and asset tracker customers will ask what happens when someone blocks or fakes GPS. This guide helps a product manager or engineering lead answer: what the two attacks are, what US law says, what a small LTE and GNSS tracker can detect, what it cannot prove, and how firmware and the backend should respond. It covers defensive design only. Figures and rules come from the linked sources, as of November 2026, and we ran no tests for this article.
What is GPS spoofing, and how is it different from jamming?
Spoofing sends signals that imitate real satellites, so the receiver computes a wrong position or time and reports it as normal. The device may notice nothing. That makes spoofing the harder problem, because a healthy-looking wrong fix flows straight into maps, geofences and reports.
Jamming fills the GNSS band with energy so the receiver cannot hear the satellites. The tracker loses its fix or takes much longer to get one, so the device usually knows something is wrong.
GNSS signals arrive very weak. The u-blox MAX-M10S datasheet lists a tracking sensitivity of –167 dBm and a cold start sensitivity of –148 dBm, measured with a good external LNA at room temperature (MAX-M10S datasheet R08, as of November 2026). At those levels, a small nearby transmitter can matter.
Tracker makers also meet self-interference. A u-blox white paper explains that the upper L band used by GNSS (1559 to 1610 MHz) sits close to the 1800 and 1900 MHz cellular bands, so a tracker's own LTE modem can degrade its GNSS reception (u-blox RF interference white paper, as of November 2026). Your own transmitter can trip the same flags as a jammer. Harmonics of the 700 MHz LTE uplink bands can also land near GPS L1. See LTE desense of GNSS in small trackers for that arithmetic and the design side.
Phone apps that fake location in software are a separate topic, since nothing is transmitted. A tracker should take its position from its own receiver, never from a companion phone.
Is GPS jamming legal in the US?
No. The FCC treats jammers, including GPS jammers, as devices that can never be authorized. This is an engineering team's summary of the texts we read. It is not legal advice.
| Topic | What the source says | Source |
|---|---|---|
| Marketing and sale | Federal law prohibits marketing and selling jammers, including GPS jammers. Jammers can never be authorized, so they cannot be marketed in the US except for authorized US government use. A disclaimer that puts the burden on the buyer does not protect the seller. | FCC Enforcement Advisory 2011-03, as of November 2026 |
| Operation | Use is illegal without express authorization, even on private property, in a vehicle or in a residence. Only federal agencies can apply for authorization. | FCC Enforcement Advisory 2014-05, as of November 2026 |
| Import | Buying a jammer abroad and shipping it to the US makes the buyer the importer of an illegal device. Imported jammers can be seized at the border. | FCC Enforcement Advisory 2014-05, as of November 2026 |
| Penalties | The 2011 advisory listed up to $112,500 for a single violation. The 2014 advisory listed up to $122,500 for any single act, plus seizure and criminal sanctions including imprisonment. | FCC advisories, 2011 and 2014, as of November 2026 |
| Consumers | Using a GPS blocker or other jamming device is a federal violation. There are no exemptions for use in a business, classroom, residence or vehicle. | gps.gov jamming page, as of November 2026 |
Two points matter for trackers. The 2014 advisory names disabling unwanted GPS tracking as one thing jammers do, and still says use in a vehicle is illegal. A fleet customer may meet drivers with blockers, and your tracker should notice and report it. And never design a blocking feature into your own product, even as a privacy option.
What can a small tracker detect on its own?
A tracker can draw on the receiver's RF readings, each satellite's signal, the plausibility of position and time, and other sensors. The table uses the u-blox M10 interface description as the worked example because its fields are public (u-blox M10 SPG 5.10 interface description R03, as of November 2026). Other receivers use other names, and some expose less.
| Signal | What it tells you | Where it comes from | Other causes |
|---|---|---|---|
| Receiver jamming state | The receiver's verdict: no significant jamming, interference with the fix still OK, or interference and no fix. | jammingState in UBX-MON-RF. The M10 interface description says firmware that supports UBX-SEC-SIG reports this field as 0 and moves it to SEC-SIG. | Your own LTE transmitter, a DC/DC converter or clock, a poor antenna match. |
| Gain, noise and CW level | Strong energy in the band moves the gain control and raises the noise floor. A narrow tone shows up as CW. | UBX-MON-RF agcCnt (percent of maximum gain, 0 to 8191), noisePerMS, cwSuppression (0 none, 255 strong). | Board harmonics, a new enclosure or antenna, your own transmit bursts. |
| C/N0 per satellite | All satellites dropping together points to the radio environment. One or two dropping points to blockage. | Carrier-to-noise density ratio in dBHz, per satellite in UBX-NAV-SAT and per signal in UBX-NAV-SIG. | Indoors, a bag, a metal surface, a body. |
| Receiver spoofing state | Whether the spoofing detector fired in this navigation epoch. | UBX-NAV-STATUS spoofDetState: 0 unknown or off, 1 none indicated, 2 indicated, 3 multiple indications. | A 1 does not mean the receiver is not spoofed, per u-blox. |
| Position or time jump | The fix moves farther than the device could travel, or GNSS time steps away from network time. | Your firmware or backend, comparing fixes with a speed limit set for the product. | City multipath, a first fix after long sleep. |
| Cell or Wi-Fi disagreement | The GNSS fix sits far from the area implied by the serving cell or nearby access points. | Your backend and the location service the product already uses. | Coarse rural cell location, moved access points. |
| Motion disagreement | The fix moves while the accelerometer reports no motion. | An accelerometer with activity and in-activity interrupts, such as the Bosch BMA400. | Steady vehicle travel can look still to a simple threshold. |
Check that the receiver features are on
The MAX-M10S datasheet lists jamming detection and reporting and spoofing detection and reporting among its security features. A datasheet feature is not yet a firmware feature. In the M10 interface description, CFG-ITFM-ENABLE, the item that turns on interference detection, defaults to false. Its broadband and CW thresholds default to 3 and 15, and an antenna setting tells the monitor whether the antenna is active or passive. Read the defaults for your receiver and firmware version, then set them on purpose (M10 interface description and MAX-M10S datasheet, as of November 2026).
Use more than the receiver's verdict
The receiver sees only radio signals. Firmware and the backend add context: a fix that jumps farther than the product can travel, a fix far from the cell or Wi-Fi area, a fix that moves while the accelerometer is still. The Bosch BMA400 offers on-chip activity and in-activity interrupts, and its datasheet gives an overall device current of 4 µA for its step counter (BMA400 datasheet revision 2.3, as of November 2026).
Consider authenticated signals
Galileo OSNMA lets a receiver confirm that the navigation message on the E1-B signal came from the system and was not modified. The Galileo GSC service site says the OSNMA Initial Service was declared operational on July 24, 2025. The receiver must store certified key material and synchronize to Galileo System Time first (GSC OSNMA page, as of November 2026). Ask whether your receiver supports it and how the device keeps its key current.
What can't a tracker detect or prove?
- A clean flag is not proof. u-blox states that a spoofing state of 1 means only that the detector did not fire in that epoch. The detector triggers most at the switch from real to fake signals, so a device that wakes after the switch may see nothing odd (M10 interface description, as of November 2026).
- A sleeping tracker sees nothing. Interference that starts and ends between wake-ups leaves no trace. The report interval sets what you can see.
- Jamming and spoofing can look alike. Both can move gain, noise and signal strength. Treat the receiver's label as a hint and log the raw readings.
- Your own radio can look like an attacker. The u-blox white paper notes that a strong input can saturate the LNA, and that one mitigation is to alternate GNSS reception with cellular transmission. Antenna layout matters too, as covered in GNSS antenna placement in small trackers.
- Cross-checks are coarse. Cell and Wi-Fi precision depends on the service and the area. A tight threshold causes rural false alarms. A loose one misses a spoof that moves the fix a short distance.
- A tracker cannot find the jammer. One small device can report that interference is present. It cannot reliably locate the source.
How should firmware and the backend respond to an alert?
Write a defined action for each state into the product requirements, and test each one on the bench.
| Condition | Device action | App and backend action |
|---|---|---|
| Jamming warning, fix OK | Keep the fix, flagged as degraded. Attach jamming state, gain and C/N0 to the report. | Show the location with a degraded label. Count events per device and area. |
| Jamming critical, no fix | Send cell or Wi-Fi location and say so. Keep a short buffer of RF readings from before the event. | Show the last good fix with its time and the coarse location. Alert if the product promises it. |
| Spoofing indicated | Keep the last trusted fix. Send the new fix in a separate field marked suspect, with the cross-check results. | Do not move the map pin or fire geofence events on a suspect fix. |
| Jump with no receiver flag | Flag the jump. Take a fresh fix and a cell or Wi-Fi check before trusting it. | Hold geofence events until a second check agrees. |
| Flags during your own LTE transmit | Log transmit timing next to each flag. | Keep these out of customer alerts and fix the design. They are not attacks. |
Protect the detectors themselves. The MAX-M10S datasheet lists configuration lockdown, signed messages and secure boot (MAX-M10S datasheet R08, as of November 2026). Use them so nobody can quietly turn detection off in the field. For a wider risk process, NIST IR 8323 Rev. 1 (January 2023), the Foundational PNT Profile, applies the NIST Cybersecurity Framework to systems that depend on positioning, navigation and timing (NIST IR 8323 Rev. 1, as of November 2026). It is voluntary.
Keep bench testing within the law. The FCC texts above make operating a jammer illegal without federal authorization. Use conducted tests into the receiver input, shielded enclosures and simulated scenarios your test lab approves, and ask counsel before any test that radiates.
What should you ask your hardware team?
- Which jamming and spoofing outputs does our receiver firmware actually expose?
- Is the interference monitor enabled in our configuration, and who chose the thresholds?
- Do the flags fire during our own LTE transmissions on the bench? What is the false alarm rate with no attacker?
- Which readings ride along with each location report?
- What does the backend do with a suspect fix, and with geofence events?
- Do we compare GNSS with cell or Wi-Fi location, and what distance counts as a disagreement?
- Does our receiver support Galileo OSNMA, and how does the device keep its key current?
- Are receiver settings locked and firmware signed, so detection cannot be turned off in the field?
- Does every tamper claim in our marketing match what the device can really detect?
For the wider tracker program, see LTE and GNSS tracker development.
What else do teams ask about GPS spoofing and jamming?
Can I add a GPS blocker to my product as a privacy feature?
No. The FCC says jammers can never be authorized and cannot be marketed in the US except for authorized US government use, as of November 2026 (FCC Enforcement Advisory 2011-03). Give users a location pause in software instead.
Is GPS spoofing illegal in the US?
The FCC advisories we read address jammers by name and do not discuss spoofing transmitters. Section 333 of the Communications Act bars willful or malicious interference with the radio communications of any licensed or authorized station, or of one operated by the US Government (47 U.S.C. 333, as of November 2026). Ask counsel how it applies to a specific case. This is an engineering summary. It is not legal advice.
Where do I report suspected GPS jamming?
gps.gov says to report GPS interference to the U.S. Coast Guard Navigation Center and/or the FCC, as of November 2026 (gps.gov interference page). For jammer use, sales or imports, it points to an FCC complaint (gps.gov jamming page).
Can Duobay help us design interference and spoofing alerts into a tracker?
Duobay develops custom LTE-M and Cat-1bis trackers for US companies, and the client receives the firmware source. We do not take government, defense or FirstNet projects, and we do not publish prices. A paid Gate 0 Feasibility study is where receiver choice, alert logic and a bench test plan get scoped. Tell us about your tracker and we will explain how it works.
Sources. All accessed November 5, 2026. Re-read them before you rely on any figure.
- FCC Enforcement Advisory 2011-03, DA 11-249, February 9, 2011: https://docs.fcc.gov/public/attachments/DA-11-249A1.pdf
- FCC Enforcement Advisory 2014-05, DA 14-1785, December 8, 2014: https://docs.fcc.gov/public/attachments/DA-14-1785A1.pdf
- gps.gov, information about GPS jamming: https://www.gps.gov/information-about-gps-jamming
- gps.gov, spectrum and interference issues: https://gps.gov/spectrum-interference-issues
- 47 U.S.C. 333, U.S. Code 2023 edition on govinfo.gov (GPO): https://www.govinfo.gov/content/pkg/USCODE-2023-title47/html/USCODE-2023-title47-chap5-subchapIII-partI-sec333.htm
- u-blox M10 SPG 5.10 interface description, UBX-21035062 R03, June 27, 2023: https://content.u-blox.com/sites/default/files/u-blox-M10-SPG-5.10_InterfaceDescription_UBX-21035062.pdf
- u-blox MAX-M10S datasheet, UBX-20035208 R08, January 30, 2026: https://content.u-blox.com/sites/default/files/MAX-M10S_DataSheet_UBX-20035208.pdf
- u-blox white paper on RF interference and GNSS performance, 2020: https://content.u-blox.com/sites/default/files/GNSS_Interference_white_paper_FINAL.PDF
- Galileo GSC, OSNMA service page: https://www.gsc-europa.eu/galileo/services/galileo-open-service-navigation-message-authentication-osnma
- Bosch Sensortec BMA400 datasheet, revision 2.3, July 2025: https://www.bosch-sensortec.com/media/boschsensortec/downloads/datasheets/bst-bma400-ds000.pdf
- NIST IR 8323 Rev. 1, Foundational PNT Profile, January 2023: https://csrc.nist.gov/pubs/ir/8323/r1/final
If you want interference and spoofing handling planned into your tracker from the start, tell us about your device.
Planning a tracker? Tell us what it needs to do. A Duobay engineer replies within 1 business day. Send a project brief →