Underground lawn sprinkler system filled with gasoline.
The fictional UA-571 C Sentry Gun from
Aliens (1986) comes to mind.....
^ That sequence was cut from the theatrical version, but I remember seeing it when I was younger, on network TV. It made that section of the movie so much more tense for me, seeing that counter run down.
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Back on-topic:
One interesting article I remember reading somewhere -I will try to find the source and post-up here if-successful- was a series of interviews with various ex- and current thieves who specialized in breaking into residential homes.
What surprised me was that their answers were
not consistent, as many "advice" articles instead tend to be, which tends to present X or Y defensive measures as ones that "work/work better" versus others.
Instead, in these interviews, what one thief would say is their #1 turn-off would often be completely negated by another, who suggested that it never hindered his efforts.
To me, this variability goes to show that home-security truly needs to be a multi-layered plan as outlined in
@Talyn 's cited article above. Everything from landscaping/lighting to window laminates, hardening of entryways, and alarms - to the choice of family pets - can all have an impact on not only target selection, but also how much warning/response-time one may have, should the resident(s) be so unlucky as to be the target of a home invasion instead of just a burglary.
A consideration that I would like to specifically point out is the relative scarcity of home-invasions that occur to the "average Joe/Jane," versus the likelihood of the home being unoccupied and burgled. This not only has implications in terms of what defensive measures should be seen as primary, but also necessarily impacts the safe-storage needs of our firearms and other defensive weapons, as well as highlights the importance of being cognizant that our risks do not simply dissipate into vapor as we pull into our driveway or even as we open the outer door to the home we return to from work or errands. Instead, we should realize that this is often one of our biggest risks of the day, particularly if we are arriving home at a time that is out-of-sync with our usual daily routines (i.e. that we surprise a burglary-in-progress).