They're easily made out of common household ingredients (water, Drano, and aluminum foil in a plastic bottle), they create an impressive explosion, and, police say, they're unpredictable and dangerous. Read the email alert and news reports about recent incidents here.

Comments
Re: Bottle bombs. Yes, it’s an old trick that has been used for many years to inflate balloons with hydrogen, to make them float. The Drano (Sodium Hydroxide, or common Lye) reacts with aluminum to create hydrogen gas. In a confined container, it will become very hot and possibly explode, causing burns or other injury. BEWARE!!