If there was ever a plant that should be planted under the bedroom window this is it. I would certainly stop anyone from escaping that way!
It is a large shrub with almost no foliage but with green winged and seriously spiny branches which have given it the names of Anchor Plant and Crucifix Plant. It hails from South America and is frost tolerant at least in pretty well all Australian areas that get frost and is also drought and heat tolerant just don’t plant it where you may back into it as I can assure you that your bum won’t be Colletia proof!
Expect a large shrub or small tree to 4 or 5 metres and plant it somewhere (such as against a blank wall) where its striking outline can be appreciated. All it really needs is sun to semi-shade and good drainage to flourish.
It might also interest you to know that it produces tiny white trumpet flowers in autumn with a sweet honey scent if you are game to get close enough.
So although it is not a plant for everyone it will certainly be a conversation starter in any garden even if it takes direct contact to get the words flowing!