The prohibition on attacking a person who is recognised as hors de combat is a rule of customary international humanitarian law (Rule 47 of the ICRC Customary IHL Study; Article 23(c) of the Hague Regulations of 1907), binding on all parties to an armed conflict irrespective of treaty ratification. For States party to Additional Protocol I, Article 41 provides its clearest treaty formulation, while Article 57 requires those who plan or decide upon an attack to do everything feasible to verify that the attack remains lawful. While these obligations have long been in force, autonomous and semi-autonomous systems operating at machine speed create a practical problem: no commonly specified machine-readable form exists through which an intention to surrender can be communicated to, and recognised by, such systems.
This paper presents HF SIGNAL 01, a candidate surrender-recognition protocol intended as a technical referent for machine-readable expressions of surrender. The protocol offers two alternative modalities: a passive visual modality, requiring no equipment, and an active electronic modality comprising two channels that must be confirmed together, a pulsating white optical signal and a radio-frequency signature. The paper does not claim operational effectiveness, adoption, or legal status. The protocol is a supplementary means of expressing an intention to surrender, never a condition of protection, and its absence permits no adverse inference. Instead, the paper evaluates the proposal against previously defined feasibility criteria for lawful operational safeguards, including technology readiness, latency, annotated datasets, and independent validation.
The assessment is deliberately conservative. HF SIGNAL 01 currently exists as a publicly documented candidate, specified in its active modality to the level of parameters that can be tested and preserved in an integrity-protected file, while the parameters of the passive modality await normative determination. It has no validated detector, no annotated dataset, no measured latency and no independent validation. Its present contribution is documentary rather than operational. The paper argues that the existence of a publicly available and integrity-protected candidate standard changes the factual context in which surrender-recognition capabilities may be assessed, transforming what was previously described solely as a technical impossibility into a documented question of design choice, review, and validation.
The paper concludes by inviting independent technical testing, dataset development, and examination within relevant international humanitarian law and autonomous weapons governance fora.
HF SIGNAL 01 is a recognition signal with channels matched to who is emitting it. Its primary channel requires no technology at all:
• The flag — a white circle on a red field, raised or displayed by the unarmed human. Like the white flag, it can be produced by anyone, anywhere, with cloth and paint — but it is specified for machine readability.
• Optical channel — 7 Hz pulsating white light, for equipped operators (vehicles, facilities, teams)
• Electronic channel — 144.0 MHz continuous FM tone, for equipped operators
Same protocol, same meaning, different levels of access: bare hands or instruments. No one is excluded from the possibility of signalling — this is the humanitarian point. A surrender signal that requires equipment contradicts itself: the person surrendering is, by definition, the one who has laid everything down. This is why the primary channel is cloth and paint. The published technical specification documents the optical and radio channels; the flag is the human-side channel of the same architecture.
Frequency reference value. The 144.0 MHz value indicated in the specification is a documented reference value, not an allocation. It falls within the 144.000–144.025 MHz segment designated for satellite use in the IARU Region 1 band plan; selection of an operational frequency requires coordination with the applicable national authorities and band plans. This determination is part of the independent regulatory validation identified in this paper as a precondition of any operational use.
HF SIGNAL 01 — Architecture Note (Human Flag Association) (V4, 27 August 2026). This note states, in one place, the architecture of HF SIGNAL 01 as the Association has published it. It amends no deposited document, alters no identifier, and asserts no obligation. HF SIGNAL 01 does not replace the white flag; it translates it. The gesture has not changed; the recipient has: a machine does not see a surrender; it detects or fails to detect a signal, and it shares no code with the white flag. HF SIGNAL 01 is a single protective function expressed through two modalities of differing accessibility: a passive visual modality — a white disc on a red field, requiring no power, equipment, licence or emission, and available to a person who has nothing — and an active electronic modality, a pulsating white light at 7 Hz together with a continuous FM tone, which presupposes equipment. The modalities are alternative expressions of the same meaning, not a conjunction; requiring all of them would exclude precisely those least equipped to signal. A confirmed signal calls for suspension of engagement and verification of status; it is never a necessary condition of protection, and its absence permits no adverse inference. The note also records the questions that remain open, including carrier frequency, emission risk, photosensitivity, separability from the protective emblems of the Geneva Conventions, and the parameters of the passive symbol, whose geometry and chromaticity are a placeholder awaiting normative determination.
International Humanitarian Law · Autonomous Weapons Systems · Lethal Autonomous Weapons Systems · Article 41 · Article 57 · Surrender Recognition · Machine-Readable Signal
HF SIGNAL 01 applies the feasibility criteria developed in: Lawful Operational Safeguards in AI Systems (Paper I) and Systemic Arrestability (Paper II). The temporal precondition governing whether such a signal can be recognised at all is developed in HFA Technical Note HFA-TN-02.