Two Lock Rule?

In article ,
"RST Engineering" wrote:

The electronics would always have been trivial to implement for an
undergrad IC circuit designer; the needed fiber optics components are
now at the Radio Shack level; and the remote signalling would be
trivial with Wi-Fi or Bluetooth technology.

I won't argue what RF technology would be best for remote signalling. I
argue that small current loops (on the order of microamperes) is much more
efficient of power AND money than optics. I'm not really sure how you
"scrape off the insulation" when the "wire" can be the chain (or better yet,
cable) itself.

My argument would be that if the wire is a current loop and is
physically accessible (and of course if the protected item is valuable
enough) a moderately competent thief can literally shave the insulation
off the side of the wire with a razor blade or Exacto knife; attach a
longer bypass wire that doesn't encircle the protected goods with a
couple of alligator clips; snip the original wire; and be home free.

This might fail -- that is, the alarm might still go off -- if the
electrical signals in the wire are high frequency enough, or the
measurement of the impedance of the wire itself, or the capacitance from
wire to ground, is sensitive enough, or . . .

But if you're using techniques that sophisticated, then the alarm is
also likely to be triggered by temperature changes, or by some large
object going by (a fork lift in a hangar), or by EMF from a nearby radio
or computer, or by . . .

A fiber loop would (in my judgment) be much less sensitive to all of the
above problems, and I believe the optical source, detector, and fiber
technology involved is now really cheap and simple.

As for the power consumption question, well, I have an optical mouse on
my desk that's been in use (putting out a lot of light, as well as
communicating constantly with the Bluetooth adaptor on my laptop) for
8-10 hours/day for many weeks now, and never turned off 24/7, on just a
couple of AA batteries.