Black widows are sneaky little buggers. They never build a web somewhere you can see the hour glass, they will always hang upside down if they build up high, or stay upright if they build down low. Like that is going to conceal them??!! The problem is prevalent here in the south. I use those sticky little pads that they are attracted to, but can't get off of once they touch the glue. Put them on each side of your doors, in your garage, basement, etc. I also use Ortho Home Defense pesticide. A gallon jug of this is only about 15.00 at Home Depot. It can be used indoors or outdoors and seems to be safe around our pets. I spray the perimeter of the house every week, and all the woodwork, windows and doorframes inside after I mop all the floors. The problem with some pesticides is it has to be injested to kill the critter. For example, the scorpion does not wash itself, so it needs a pesticide that gets into its nerve system if touched, not eaten. I'm not sure if widows wash themselves, but my remedy seems to be effective. I think Home Defense attacks the nerves when contact is made.
Hair spray works well, especially in the heat. No need to light them up afterwards, when the hair spray dries, it stiffens them to immobility, as long as you douse them. Oven cleaner kicks ass.
Its interesting to watch them twitch
. When in a pinch, use a shoe, preferably someone elses.