Noting that discussion of criminal methods is to be deprecated, lest it encourage the criminals, the following is all "old stuff" that they all know, although it may be news to the honest people.

Contrary to the notion propogated by movies and TV, breaking an auto glass seldom makes much noise regardless of the tools or method. Modern "tempered" glass, as generally used in side windows often doesn't even fall out of the frame with the inital breaking. The only sound is the single-blow "impact noise" which is about the same as one would get from hitting the nearest picket fence once with a medium sized hammer. Once the glass is broken, it can be pushed out of the frame almost silently by hand.

A common ball-pien hammer works quite satisfactorily, but due to the short handle breaking a side window with a hammer of less than about 5 oz can be difficult. It's no problem (usually) with a 7 to 12 oz hammer. The spark plug, or a large nut, or any other object that can be tucked into the end of a sock or tied to a string, can be swung against the window so that it strikes with fairly high velocity and thus delivers a fair amount of energy concentrated in a small area. It can be, in effect, a 3 oz ball-pien hammer with a 3 foot long handle - that fits in one's pocket.

Persons aware that something was happening would hear a single "bang," "thud," or "ping" when the object hits the window, but not much else. There is NO SOUND OF GLASS BREAKING in the manner of the sound effects in the movies, and nothing like the falling glass heard if someone breaks out a "wash glass" window in a house.

As to the bump key thing, anyone with the requisite knowledge to use one effectively can probably, with only a little more effort and a very slightly reduced probability of success, produce the same result with a properly bent paper clip. The bump key just makes it a little bit quicker, and very slightly more reliable.

Modern thieves generally will prefer to use the professional locksmith's "shaker pick." (Other names are used.) The "pick" has one or more points to raise the pins in the lock as the bumps pass the pins, but is attached to a handle (battery powered) that vibrates it rapidly as it's inserted and withdrawn. Guaranteed to open any common pin-lock in 10 seconds. (almost always)

Many recent model automobiles use much more sophisticated locks that are a lot more resistent to illicit entry. An example is the "double sided key" that some makers advertise as "letting you put the key in either side up." While this is a great convenience(?) in some but not all such locks it's necessary to actuate pins on both sides of the key in opposite directions at the same time to get the lock open. This does make it a lot harder, though not impossible, to "pick." Unfortunately, some "double-sided keys" simply work the same single set of pins with either side of the key - as advertised - and provide no significant improvement in theft resistance. (Hint here - your dealer probably doesn't know which kind (s)he sells.)

Electronic locks on vehicles in a variety of kinds are offered now. Most of them actually are a bit harder to defeat than the older kinds, but there remains a lot of variation in the amount of improvement obtained. A "kill switch" that shuts down the engine shortly after it's started without the proper key is considered a reasonably worthwhile protection against the thief getting far with a vehicle, although a "chop shop" thief may only intend to drive it around the corner before loading on an auto-tow truck.

For the home, there are a variety of "super-security" locks, and some of them are incredibly difficult to pick. An older style "bumper jack" crosswise in the doorway to spread the frame far enough to clear the deadbolt still works on almost any of them, and is virtually silent - unless a board breaks.

End point:

Be afraid, but it won't do a lot of good to be really paranoid.

John