Define "electric door knob." If you mean a door that opens
itself electrically, they're all over the place - as are security
locks which incorporate an electric release, and use a keypad
thumbprint scan, etc., for access.
If you look at his other question, which is basically the same
question but gives insight into his intent, it sure seems like
his idea of an "electric doorknob" is one that shocks people
when they touch it.
It's obvious why they've not been invented. IN order for current
to flow, you need two terminals. If the knob itself supplied
both, the current would be limited to a small area of the body. If
the knob is used as only one terminal, then some other terminal has
to be supplied, and you can' always count on having a convenient
metal surface where someone would be standing to supply that other
terminal. Also variables come into play, such as whether or not
the person is wearing shoes, or what type of shoes. An effective
"electric doorknob" requires that it be reliable, and it can't
be that if someone shows up with rubber soled shoes.
There's also the "minor" issues of what purpose this would serve.
Perhaps a deterrent, yet unless it supplies a lethal shock the person
would just use some other means of getting inside or getting the
attention of someone inside. I suppose some might see it as a gag,
though there might not be enough interest in that use to really
warrant the heavy design work.
Also the "minor" issue of liability. Too little current/voltage
wouldn't deter someone, which might bring lawsuits to the manufacturer
when people find the product doesn't work as claimed. Too much
current/voltage and it would be lethal, again bringing lawsuits, at
least to the homeowner and maybe manufactuer from the deceased relatives.
Of course, the "electric doorknob" has been invented, as anyone who's
seen one of the "Home Alone" films will know. Though technically I'm
not sure little Kevin actually created a working "electric doorknob"
even though the film showed it as working.
Michael
