Radio Frequency Tags -

These are a spiral shape. They can be disarmed by making a slit in them. Sometimes radio frequency tags are actually embedded in the cardboard packaging.

Electromagnetic strips -

These are a tiny strip of metal. They can usually be pulled off but if you want to disarm them, you can do so by magnetising them. They can be magnetised by waving a powerful magnet in front of the strip repeatedly for 20-40 seconds.

Acousto-magnetic tags -

These tags are a centimetre in length and width. They stick out of the box about a sixteenth of an inch. There are three metal strips going through these type of tags, one of the strips actually shrinks if you go through the sensor and it sets off the alarm. You can disarm these tags by demagnetising them.

You can demagnetise an acousto-magnetic tag by waving a regular magnet over it several times, in a different direction each time. Another way of demagnetising them would be to use one of the two magnets inside your computer. It depends on what computer you have but a lot of the time these magnets aren't needed. I took mine out of my computer and they work good because they have a North Pole and South Pole on either end and either face of the magnet. (They are able to do this because they are made of two different metals.) i.e.

North South
__+___________________-__
|____________|____________|
- +
South North

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"If I line the inside of a bag with tin foil and put a stolen object inside, will it set off the alarm?" Despite popular belief, the tin foil will not shield the contents of the bag from the magnetism. Foil will work with radio frequency tags (the ones that look like a spiral), by shielding the tag from any radio frequency (RF).

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"How do radio frequency tags work?"

A transmitter sends out a RF, the tag picks up the RF and emits its own RF that is picked up by a receiver.

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"Why would making a slit in an RF tag disarm it?"

If you make a single break in the spiral, the circuit will be open and thus can no longer produce any RF.

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"In disarming acusto-magnetic tags, what's the advantage in having a north and south pole on either end of either face of the magnet?"

When something becomes magnetized e.g. a piece of iron, all that is happening is that the magnetic atoms of the material are becoming aligned (they point the same way). The south pole of the magnet is moving the magnetic atoms in one direction and the north pole of the magnet is moving the magnetic atoms in a different direction. Because the magnetic atoms are not pointing the same way, they are not aligned and thus, not magnetized. Demagnetising the tag can be done quicker with the computer magnet because if you sweep the magnet over the tag 5-10 times, it will more than likely be demagnetised. While with a regular magnet, I'd sweep it over the tag around 30 times just to be on the safe side.

If you are still unsure that these methods work, go to your local CD shop (they usually use electromagnetic strips) and take the strip off the CD, magnetise it and stick it to somebody's back. See if the alarm goes off when they walk out.