In the case of a home invasion (that is, a serious criminal trespass in a place of residence), acting for a defensive purpose or to defend property can be a complete defence to an offence, including murder, even if the defendant's conduct was not objectively reasonably proportionate to the perceived threat [Criminal Law Consolidation Act 1935 (SA) s 15C].

The defendant must have genuinely believed that the victim was committing or had just committed a home invasion [s 15C(2)(a)].

This section is not available if the victim was an on-duty police officer [s 15C(1)(b)], or if the defendant was themselves engaged in criminal activity that might have given rise to the threat [s 15C(2)(b)], or if the defendant was substantially affected by the voluntary and non-therapeutic consumption of a drug [s 15C(2)(c)]. Drug includes alcohol and any other substance capable of influencing mental functioning [s 15C(3)]. The consumption of a drug will be considered non-therapeutic unless it has been prescribed by and taken in accordance with the directions of a medical practitioner or is available without prescription from a pharmacist and taken as the manufacturer intended [s 15C(3)].