We inspect for packages that have come open.
But, if it makes anyone feel any better, check out snopes.com on this.
Pins and needles in halloween candy has almost always been traced back to kids playing pranks on each other. There was a single case of a man doing it to trick-or-treaters, but my understanding is that pins in candy are rather obvious, and no one was hurt, other than one child being pricked.
And there has never been a case of random poisoning of halloween candy for trick-or-treaters. The case in Houston in the 70's was a man purposely poisoning his own children. There have been coincidental deaths that the media likes to jump on, but they were all either traced to disease, overdoses of drugs in the parents' home (followed by the parents trying to hide behind the urban legend), and heart failure. (None of this makes the front page, of course, after the initial sensational story - Child Dies After Eating Halloween Candy! - is published.)
Although quite a few folks in my circle don't do candy anymore, anyway. We pass out the kinds of little things you find in the party-favors aisle. (Pirate gold was very popular this evening! - So were the little dinosaurs.) I have one girlfriend who does temporary tattoos, and another who passed out those little lunchbox-sized, pre-bagged packages of baby carrots. My parents did little pre-packed bags of pretzels. Our neighbors do dimes.