Deterrents that hurt people are a different category
Locks, lights, cameras and alarms deter without injuring anyone. A separate genre of “deterrent” is aimed at hurting whoever breaks in: a concealed spike, a wired-up electric shock, a rigged door or a spring-loaded device. This article summarises three sources: section 31 of the Offences against the Person Act 1861 and section 1 of the Occupiers’ Liability Act 1984, both as published on legislation.gov.uk, and the joint 2018 statement on householders by the Crown Prosecution Service (CPS) and the National Police Chiefs’ Council. The 1861 provision is marked as extending to England, Wales and Northern Ireland; the 1984 provision is marked as extending to England and Wales only. Scotland has its own law, which is outside this article.
The criminal offence: section 31 of the 1861 Act
Section 31 makes it an offence to set or place, or cause to be set or placed, a spring gun, man trap or other engine calculated to destroy human life or inflict grievous bodily harm, intending that it may do so to a trespasser or anyone else who comes into contact with it. A person who knowingly and wilfully allows such a device set by someone else to remain in a place in their possession or occupation is treated as having set it with that intent.
The section is old, and its text includes two provisos. The first says that nothing in it makes it illegal to set a gin or trap of the kind usually set to destroy vermin. The second says that it is not unlawful to set a spring gun, man trap or similar engine from sunset to sunrise in a dwelling house for its protection. Those exceptions are part of the statutory wording, but they do not stand alone: the civil duty and the CPS position described below still apply, so the night-time proviso should be read as a narrow exception in a nineteenth-century provision, not as approval of household traps.
The civil duty to trespassers: section 1 of the 1984 Act
In England and Wales, an occupier can owe a duty to someone who is not a lawful visitor. Section 1 sets out three conditions: the occupier is aware of the danger or has reasonable grounds to believe it exists; the occupier knows or has reasonable grounds to believe that the other person is in the vicinity of the danger or may come into it, whether or not they have lawful authority to be there; and the risk is one against which the occupier may reasonably be expected to offer some protection.
If those conditions are met, the duty is to take such care as is reasonable in all the circumstances to see that the person does not suffer injury on the premises by reason of the danger. The section is framed around dangers due to the state of the premises or to things done or omitted to be done on them. It says the duty may, in an appropriate case, be discharged by giving warning of the danger or discouraging people from running the risk. It also provides that no duty is owed for risks a person willingly accepts, and that a breach of the duty creates no liability for loss of or damage to property.
The Act concerns injury, and its duty arises only where all three conditions are met. Whether a particular device or hazard brings an occupier within it depends on the facts and is a matter for legal advice.
What the CPS and police say
The joint CPS and National Police Chiefs’ Council statement, revised in 2018, addresses householders confronted by an intruder. It says that reasonable force may be used in self-defence, that a householder acting in the heat of the moment is given the benefit of the doubt, and that disproportionate force used to protect property is still unlawful. It also gives an example of conduct that would be treated as very excessive and gratuitous force which could lead to prosecution: knowing of an intended intruder and setting a trap to hurt or kill them rather than involving the police.
The statement judges a householder who reacts in the moment by what they honestly and instinctively believed necessary; the trap example is treated differently because harm is prepared in advance. The full framework for confrontations is covered in Defending Your Home Against an Intruder: What ‘Reasonable Force’ Means in England and Wales.
Devices that people confuse with traps
- Anti-climb measures. Fixed obstacles on boundaries are a separate subject, treated in Anti-Climb Systems and Boundary Reinforcement.
- Guard dogs. A dog raises its own liability questions, covered in Dogs as a Deterrent: What UK Law Actually Says About Guard Dogs and Liability.
- Warning signs. Section 1 of the 1984 Act says a warning may discharge the duty in an appropriate case, but the Act does not say that a sign makes a dangerous device safe to install.
Deterrence that carries no injury risk
Deterrents that work by making a break-in slow, visible and likely to be recorded do not raise these questions. Good locks, lighting, visible cameras and a monitored or self-monitored alarm all work alongside a call to the police, which is the first step the CPS statement gives: wherever possible, call the police.
The bottom line
In England and Wales, a trap intended to injure an intruder is a different matter from defending oneself in the moment. Section 31 of the Offences against the Person Act 1861 creates an offence for setting such devices, with narrow statutory provisos; section 1 of the Occupiers’ Liability Act 1984 sets out when an occupier owes a duty of care to people who are not lawful visitors; and the CPS and police say that setting a trap to hurt an intruder instead of involving the police could lead to prosecution. The 1984 Act does not extend to Scotland or Northern Ireland, so the civil position there is outside this article. Security that is passive, visible and connected to a police response is the safer route.
Sources
- legislation.gov.uk, “Offences against the Person Act 1861, section 31 (Setting spring guns, &c., with intent to inflict grievous bodily harm)”
- legislation.gov.uk, “Occupiers’ Liability Act 1984, section 1 (Duty of occupier to persons other than his visitors)”
- Crown Prosecution Service and National Police Chiefs’ Council, “Householders and the use of force against intruders”