Al and Ti can both be detected by many types of electronic detectors. The detectors used at most US airports, for example, will pick up both of these. Now, you're not entirely off-base thinking that these two may not be detectible. They are not detected by some types of electronic detectors. You see, there are several different methods for electronic metal detection. We had an extensive post on this subject some time ago. Some of the simplier methods don't detect Al and Ti because these metals are non-magnetic. In fact, the magnetic characteristics of these metals (and others) are exactly opposite of steel.
One common type of metal detector involves having the subject walk through a coil of wire. Any coil of wire, even a very large one, has an electrical characteristic called "inductance". The inductance depends primarily on how many turns of wire are in the coil, the spacing of the turns, the diameter of the coil, and the material in the middle of the coil. In the detector, the number of turns, diameter, and spacing all remain the same, but the material in the middle changes as you walk through. If you put steel or iron in the middle, the inductance goes up dramatically. Put Al or Ti in the middle and it will go down dramatically. Simple detectors detect only an increase in inductance. More sophisticated ones detect a change in inductance either way.
The detector in this gentleman's bank's door, however, was not this type since it obviously is built into a moving door so it can't contain a fixed inductor. But, given that this is obviously a fairly sophisticated device (and devilishly clever), my guess is that it would pick up Al and Ti too. But, of course, the bank's primary concern is guns and guns are primarily made of steel. My guess is that the guard can release the mechanism allowing the door to go backwards to allow anyone who might have some object to large for the slot to back out, leave their sword (or whatever) in the car, and come back. The interesting question for me would be someone with stainless steel pins or plates inside their body, an artificial hip joint or two, etc. How does this person get into the bank? Strip naked there in door?
I used to work for a large defense contractor in a very secure facility. If you weren't carrying anything (boxes, etc.) you could enter the fence around our building from the employee parking lot (which you had to enter via a guarded gate anyway) through a "turnstile". This device, sort of like a revolving door, had a slot you stuck your badge into and a mirror you looked into. There were two TV cameras inside and a bar-code reader. The reader read the code on your badge. The first camera looked down at your badge and the picture and name on it. The second camera looked through the partially silvered mirror at you. If the computer said your badge was ok and the guard at the security office thought you resembled the picture on your badge, he'd buzz you through. One guard at a central station could run a number of turnstile gates at one time, a considerable savings to the company. But, the turnstile device had a rachet mechanism and could not go backwards. Once you went in, it locked and you had to wait for the guard to release it and let you through. Every once in a while, someone would go in not realizing that they had no badge or the wrong badge (husband and wife both worked there and grabbed the wrong badges that morning, for example). Sometimes, someone with a badge that was not cleared for that area would try to come through not realizing that you had to have a special clearance to enter our building. Those people just had to stand there locked in the turnstile until a guard arrived from the security office with the key. Our building was about a mile (this was a very big installation) from the security office. The guards on duty in our building did not have a key for the turnstile. Furthermore, there was a major public road that ran through our facility (we were on either side of the road), and the security office was not only a mile down the road, it was on the other side. In rush-hour, it could take a guard an hour or more to get to our turnstile with a key. On day, one of our colleges tried to enter through the turnstile but found himself with his wife's badge. The turnstile locked and the guard refused to release it. It was a very cold day, but since this fellow, an older fellow, had not intended to be more than a couple of minutes at most from his car to the building, he hadn't brought a jacket. He got a bit paniced locked there inside that confined turnstile in the bitter cold and actually had a heart attack right there. One of the people waiting realized this and picked up a phone mounted along the fence that rang directly to the company fire department (remember, this was a major defense contractor, our facility was over a mile long and had its own fire department). The fire station was right across the street from us, so they arrived instantly, but could do nothing since this poor fellow was locked inside the turnstile. By this time, word had spread and several of our machists arrived from inside the building with a very powerful cutting torch. They cut that turnstile to bits in seconds and freed the man to the inside of the fence where they were, then they cut the fence to let the paramedics get to the man. This, of course, set off alarms. The guards from inside the building came and tried to stop the men from cutting, but the crowd gathered (I was on the outside) restrained the guards. Everyone who was on the inside of the fence and involved (including the paramedics who came through the cut fence) were briefly fired for interfering with and violating security. They were, of course quickly and fully reinstated when the news got out, of course and, in fact, given comendations for quick thinking to save the man's life.
------------------
Chuck
Balisongs -- because it don't mean a thing if it ain't got that swing!
http://www.4cs.net/~gollnick
