removing security screws

What is the best tool to remove security (one way) screws from window bars? The device I bought for $15 at Home Depot just slides off the screws and is basically useless. (It sort of resembles a miniature lug nut wrench with a little washing machine agitator inside. It is used with a power drill.) Suggestions appreciated. Paul in San Francisco
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Paul MR wrote:

If you don't mind ruining the screw, a left-handed drill bit in a reversible variable-speed electric drill does a good job.
Bob
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Paul MR wrote:

If I just have a couple to remove, I use a small set of visegrips. Where it is convenient, I also have used a cut off blade on a dremel tool to make a slot, then use a straight screwdriver. I will send a guy around to grind all the slots, then we go around with a drill driver to remove the screws. That works well when you have a lot of them to do.
--
Robert Allison
Rimshot, Inc.
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