about metal detectors?
969954
I think that metal detectors just work by setting up a magnetic field. When the apparatus move over a location that has a magnetic material a flux is produced that induces an electric current in the metal detector, activating a sensor.\n\nIf this is the case (i'm 95% sure it is), then the only factors affecting it's quaility would be within the machine itself as far the smallest current that activates the sensor.\n\nHeat and moisture would not change the magnetic field (moisture might theoretically alter the detectors magnetic field a little bit, but certainly not enough to measure). The both give the same result.
188114
Passive Infrared Motion Detectors- These detectors are also known as PIR detectors. The technology they utilize is “passive infrared”. The device is mounted on a wall or in the corner of a room. It sends invisible fingers out into the covered area in several layers.\n\nThe top layer goes the furthest and averages about 60 feet straight ahead and 35 feet on the sides.The center layer of beams spreads the area about mid way and the bottom layer sweeps the room closest to the detector.\n\nThese beams individually measure the infrared temperature of what ever they land on and look for a clash of temperature against that point. For example if a beam lands on your couch and knows what temperature it is, when you walk in front of the couch your temperature is different and causes a violation. You would be hard pressed to match the temperature of everything in your home as you walk about and that makes motion detectors hard to compromise.\n\nPassive motion detectors have a microchip in them that will adjust the device for slow and methodical temperature changes. This way as your room warms up and cools down during an armed alarm period, you will not get a false alarm.\n\nSome motion detectors are designed to be mounted in the ceiling and spread a 360-degree cone downward. Some are recessed to replicate an electric outlet and various other combinations are available for the James Bond like clients. Most often the device is an aesthetically pleasing small device that is mounted 5-7 feet high in the corner of a room.\n\nPassive infrared motion detectors will not see through walls or windows as they will consider touching one of them as their final destination and begin calculating the temperature. The beams project forward only and will not bend around corners. If your device is placed where a beam can go into an area with an opened door, it will protect the interior of that area as well. Once the door is closed the beam will terminate on that door.\n\nMotion detectors are not going to protect every square inch of your home or business unless you invest in many of them to accomplish that. Instead you should intelligently place them as an interior trap in an area or areas most likely to be violated by the creep or creeps that want to take your belongings or worst off violate you personally. Usually one placed properly on the main floor and one on the lower level if you have one, will serve as good traps. Stairways are often a good thing to consider when placing the device, due to the fact that you will prevent unauthorized passage from one floor to the next.\n\nSee linked article for more info such as how some motion detectors are "pet immune".
835841
I do not have a metal detector but I would think that bottle caps, rusty cans and old nuts and bolts far outweigh the number of priceless jewels out there. On the other hand, does something have to be vaulable to be cool? I think some of those rusty cans and bottle caps may turn out to be pretty interesting.
681738
Not unless you have radar absorbing paint which the government would love to have too.  I was picked up on a 10 speed bike trailing all kinds of foil to mask me but I was still picked up and clocked by police radar gun.  If you find a way post it.  I want to know that trick.  You can overload them with powerful transmitters, the radar reads false speed like 200mph which is not reliable for court,especially when I drive a 1972 VW bug, but they are illegal.  Plans on Internet and part from Radio Shack
916216
Radar detectors are banned in Virginia.\nRadar detectors and radar jammers are illegal in the District of Columbia.\nRadar jammers are illegal in Oklahoma, but radar detectors are legal.\nIn New York, radar detectors are illegal for commercial vehicles over 18,000lbs.\nIn IIlinois, radar detectors are only regulated in commercial vehicles.
467769
This is an important question - the health effects of microwaves.  Some comments: Lead is not necessary.  Lead stops ionizing radiation like x-rays, but for reflecting microwaves, any conductive metal will do; aluminum is the most commonly used for microwaves, and is a better conductor than lead.\n   Metal mesh will work, just like in a microwave oven, but the problem is, it will only be really effective if you build a sealed box.  If you only cover the windows, the microwaves will come through the walls, floors and ceiling.  Also, at the joints between sheets of metal mesh, you need to have a continuous eletrical connection.  Any seam which is unconnected over a few inches will allow power in.  A large seam may behave just as if the mesh is not there at all.  (This is why a cell phone will sometimes work in an elevator, and sometimes not)  \n    I would think that using aluminum adhesive tape running down the seams of the mesh on both sides would work. \n    Anything that only covers one wall or less may help, but it may not help at all, as microwaves bend around the edges of shields, and also are reflecting off all the other parts of your building.  Any non-sealed metal mesh structure will interact with the radiation field as a open metal resonator in a very complicated way, which is hard to predict and depends on the specifics of the metal geometry, the direction and frequency of the radiation, and all the collection of reflectors in your building (pipes, wiring, window screens, reinforcing bars in concrete).  However, if the metal mesh box is truly sealed and has no open seams whatsoever, you are 100% safe.  People build these out of mesh for low-noise testing chambers, but they are hard to build, especially around doors and inlets for electrical wires and plumbing.  It really is a huge undertaking for a non-professional, sorry.\n     One final comment: you can take some comfort in the fact that if what you see outside your window are dishes, they are highly directional antennas.  Typically, they direct nearly all of their power in a cone within 1 to 4 degrees angle of the satellite or receiver where they are aimed.  Typically, stray radiation (called sidelobes) are 30 dB lower, meaning that the power radiated in other directions is one thousand times lower.  \n      Cell phone towers, however, which do not look like dishes, but an array of typically three or more panels, are not directional, and spray alot of microwave power in all directions.\n     Is there a health risk?  I'm director of a microwave engineering firm, and I don't know the answer for sure.  Just not enough data.  In my own laboratory, however, I always take all precautions to make sure no one is ever exposed to any microwave radiation, just in case.  There are national standards which govern the equipment outside your window, which do specify a maximum 'collateral' radiation level, which is deemed to be safe, based on what data does exist.  I would tend to believe that it is extremely likely they are correct about these levels being safe (safe meaning less likely to hurt you than the air pollution you breathe, the chemicals in the products you use, etc.), but we cannot be 100% sure.\n    Personally, I would be fine with living in an apartment looking out on a bunch of dish antennas, but if it was directly adjacent to a cell phone tower or building with cell phone array on it, I would not want to expose my family to it, and would move out.
323880
I'm not sure what your question is.  A thermoelectric thermometer should have a sensor made of two metals.  It's a thermocouple.  Obviously the heat capacity of any metal is very low.
700634
i heard there are tiny metals ranging in size between\nmicrodots and pieces of wire 1/3rd of an inch.
975165
It depends on the centre frequency and bandwidth of the IR detector.  Glass will absorb certain IR frequencies, very often IR detectors use this as they do not wish to see beyond windows which would cause false alarms.
36557
In 1881, Alexander Graham Bell invented the first metal detector. As President James Garfield lay dying of an assassin's bullet, Alexander Graham Bell hurriedly invented a crude metal detector in an unsuccessful attempt to locate the fatal slug.
211316
Visit www.goldprospectors.org. You will find lots of valuable info and links about all types of gold prospecting and metal detecting. Also their bi-monthly magazine is full of articles on locating lost gold.
803774
The metal sheets are a part of the safety protocol on a construction site. The prevent accidents and injuries caused to general public due to activities on site. Most of the machines and processes are dangerous.
737567
Sometimes it's not illegal to sell or possess certain items, but it is illegal to use them.  I think in most cases radar detectors fall under this category.\n\nIn particular, they are illegal to use in Arkansas. Sorry about that.
960848
The detectors in stores are activated by special tags that are inside items. These tags respond to a radio signal that is generated by the sensor. When the item is placed on the part of the checkout that buzzes, there is a capacitor in the tag that gets magnetized (or demagnetized) , and the spacing of the metal changes, cancelling the effect of the capacitor.\n\nIf the detector is going off, then it means that you have some item with you that is responding to the RF field setup by the detector. It 's possible that some electronic item is responding, or perhaps you have one of these tags that wasn't properly magnetized. Some stores will let you through if the sensor alerts as long as you have a receipt. If they do this, and you carry the tag, it will go off when you go through.\n\nA friend of mine had one such, and he used to put it in his shoe, and, wearing a tank-top, shorts and sneakers, have fun setting off the sensors.
899236
LOL, nope most churches don't have any metal detectors. So, please carry whatever weapons you feel you need to be safe with. LOL  I don't go to any church or mosque, but I'm sure if you wore a mask and cape they'd like you better when you pick a place you'd like to visit. Plus it would make your use of weapons more theatrical. Have fun. LOL
311539
Radio Shack sells FM frequency detector.  Since most listening devices work on FM frequencies, it should be pretty simple to locate.  You can also use a Near Radio Field Meter.
1133434
You just have to install them.  Double sided tape would do the trick if that's the way you wanted to do it.\n\nAnd the detectors would be wailing way before the adhesive melted, in my humble opinion.