High Tech Alarm

My terrace has been invaded three times on occassions that I know about, missing items - a beach chair and barbecue spits - evidencing these incursions, and maybe other occassions that I don't know about. The last occured at 5am a few weeks ago, when I saw through the curtians of the French windows, the silhouette of a person trying to get through the bars which separate the terrace from the balcony, my furious shout of GET THE FUCK OUT!! surprised him enough to, indeed, get the fuck out. When I reported this to the owner of the aparment he just offered to reinforce the bars, but I don't want the bastards to get on to the terrace in the first place. Electric fencing the terrace will cost me R$620, a movement detection alarm, R$680. So I've rigged up a sophisticated high-tech alarm system myself. A large one litre beer bottle, I had to drink the beer first of course, twelve metres of fine nylon fishing line. I've placed the bottle attached to the line on a wall and secured the other end to the far wall, the line is about a metre from the ground and invisible at night. Two of these, one covering the terrace length and the other covering the width where a possible invasion may occur. A smashing beer bottle at night will wake me instantly, what I do then, I'm not exactly sure, hopefully the invader will be shocked enough just to bugger off there and then. What I would really like of course is to have the bottles filled with explosives and nasty pointy things.