When the exterminator told us that he was going to charge us $50/a piece to install bird flashers as part of a larger package, I gave him the old "I have to check with my wife first" excuse, then promptly looked it up on everyone's favorite search engine. When I realized what they amounted to rather than pay the $11 for each one on line, I got a little indignant and decided to build my own. (I still let the guy spray for bugs.) As you can see, they probably aren't worth $50, $11, or even $5 total. I'd estimate I spent a hair less than a dollar for each so far, with parts left over. The tricky part is hanging it, so if you have qualms about using tools on ladders then maybe you'll find the exterminator's price worth it. Before we begin, remember to observe all safety precautions you see on your tools, your ladder, your scissors, etc. Be careful on that ladder, wear safety glasses, and if it ever crosses your mind that you're about to make a decision that could turn you into a Jeff Foxworthy punchline, come down.

The video here shows about how it works. All natural, solar and wind powered, doesn't hurt the dog's ears or interfere with bat navigation, pretty darned effective so far.

Step 1: Step One: Materials

Pretty straightforward stuff here. For each flasher you will need:

12-24" of 2" wide (actually 1 7/8" wide) Iridescent Craft tape
1 Size 5 Barrel Swivel (in the fishing supplies)
1 Jumbo Paper Clip
1 Screw-Eye (size unimportant as long as you can get the safety-pin opening of the barrel swivel through the eye without binding.)

Tools include scissors and a drill (optional, if you want to drill a pilot hole for the screw eye.)

Step 2: Step Two: Metal Work

Bend the paperclip into a triangle similar to the jumpers you made out of paperclips as a kid, but with the jumping mechanism severely flattened. (See the photo if you never did this as a child.) Slide the fixed end of the swivel through one of the open "legs" and leave it at the corner opposite the two-pronged edge of the paperclip triangle. This doesn't have to be a perfect equilateral triangle. In fact, having a little imbalance to the sides probably contributes to the effectiveness (see the last step.)

Step 3: Step Three: Assembly

Cut your length of tape on a clean(er than I used here) surface. You can make this tape any length, so cut twice the length of tape as you want the flasher to descend from your roof. About 6-12" is a good target though, as shorter lengths aren't as annoying to the birds and longer ones present unmanageable lengths of tape to work with. Try to cut both sides at as close to a right angle as possible (so that you have a very wide, proper rectangle) to make later steps easier.
Slide the tape through the center of the paperclip triangle from the previous step such that the sticky side is facing the "open legs" of the paper clip. Loop the tape so that it forms two equal halves on either side of the paperclip "joint."
Very carefully touch the facing corners of one side of the tape to one another so that the top and the outside edges align. Adhere the halves of the tape to one another as flat and true as possible. (Not that the birds will mind, you just want to make sure you're not catching flies with this thing-that would be ineffective. Also there's probably some longevity advantage to sealing the adhesive sides together.)
Flatten the halves of the tape down to the paperclip end, and use the tape to squeeze the paperclip legs together as much as possible.

Step 4: Step Four: Attach the Screw Eye

Hook the open end of the barrel swivel through the screw eye and close the latching mechanism.

Step 5: Step Five: Hang It

Generally you want to put one of these on every "outer corner" of your roof, so that a bird can see one wherever they perch to peck. Inner corners aren't as useful for this purpose. Where I have the one in the photos isn't perfect, as the gutter and trim obscure the view somewhat on the side, but my wife would kill me if I put a screw eye in our new seamless gutters.

As mentioned, be careful on the ladder. You can drill a pilot hole before installing if you choose.

For more effectiveness, consider rigging an arm made of wire hanger or a book shelf support to make the flasher more visible and more "floppy" in the wind. Part of what makes it annoy the birds is the motion, so if it's not in a position that gets wind, the birds might conclude it's not a threat.