The Criminal Law (Defence and the Dwelling) Act 2011, used as a defence for the first time in Martin Keenan's trial, allows people to use reasonable force if they find an intruder in their home.
It was introduced in the wake of the Padraig Nally case, which sparked a debate about the rights of home and landowners to defend their properties.
Mayo farmer Mr Nally was charged with murder after he shot dead John 'Frog' Ward, a notorious criminal he found trespassing on his property.
He was acquitted of murder but sentenced to six years in prison for manslaughter in 2005.
The conviction was quashed by the Court of Appeal and he was cleared of manslaughter at a subsequent retrial.
In the wake of the case, rural interest groups sought clarity on the rights of a person to protect their home.
Although that right had long been recognised by the courts, the then justice minister Alan Shatter introduced the act to provide further clarity.
It removed an obligation on householders to retreat and allowed them to stand their ground and use reasonable force against intruders.
Under the act, a jury cannot have regard to the fact that a householder who comes across an intruder may have had an opportunity to retreat.
It has to consider only whether the force used in tackling the intruder was reasonable and justified.