Because the tag responds mechanically at a low frequency, and low-frequency magnetic fields pass through and around materials that block higher-frequency ones.

At 58 kHz the field is magnetic rather than radiative, and metal detunes it far less than it does a radio-frequency label's antenna.

Liquids absorb energy strongly at higher frequencies and much less at this one, which is why bottled and canned stock is manageable.

The tag's response is a physical resonance that continues briefly after the transmit burst ends, so the receiver listens in a quiet window with the transmitter off.

That listening window is what gives the technology its noise immunity as well as its material tolerance.

It is not immune, though. A label stuck flat on solid foil still performs poorly, and a spacer or a different placement remains the answer.

The widest of the common EAS technologies - which is the main reason large-format stores choose it.

Published widths assume favourable tag orientation and a clean electrical environment, so the usable figure in a real entrance is lower.

Metal shopfront framing, floor reinforcement and nearby fixtures all reduce it.

Where the entrance exceeds the reliable width, additional pedestals are placed in the opening to create two or more detection zones.

Multiple pedestals need synchronising so they do not interfere with one another, which means an interconnection between them.

Have the supplier confirm coverage for the measured opening with the intended tags, in writing, rather than relying on the brochure figure.

Noticeably more per label, because the tag contains a resonator strip rather than a printed antenna - and at volume that difference is the dominant running cost.

A radio-frequency label is a flat printed circuit on paper and is extremely cheap to produce.

An acoustomagnetic label contains a metallic resonator and a bias element, so it is thicker, less flexible and more expensive.

On a store tagging tens of thousands of items a week, the annual difference is material and should be modelled rather than estimated.

Against that, fewer pedestals may be needed for a wide entrance, and detection reliability on difficult stock is better.

The thickness also matters practically: an acoustomagnetic label is visible and palpable through thin packaging in a way a flat label is not.

By demagnetising the bias element, which stops the resonator responding - and it is worth verifying rather than assuming.

The deactivator applies a field that removes the magnetic bias the tag needs in order to resonate at the detection frequency.

It is fast and works through packaging, which suits integrated scanner-deactivators at the till.

Because the mechanism is magnetic bias rather than physical destruction, a deactivated label can in principle be re-biased by a strong magnet.

That is not a common attack, but it argues for deactivation verification at the pedestal so a live label passing the door is flagged as such.

Check the deactivator's range against the products. A label buried in the middle of a bulky carton may need the item passed closer than the operator expects.

Pulsed sources at similar frequencies and, most commonly, another acoustomagnetic installation nearby - continuous electrical noise affects it less.

The transmit-and-listen cycle gives good immunity to steady noise from lighting and motors.

A neighbouring store's system operating through a shared wall can trigger or mask detection, and synchronising between installations is sometimes necessary.

Large moving metal - shutters, escalators, trolley collection - can produce transient responses.

Electronic equipment switching at related frequencies is worth checking during the site survey rather than after installation.

The symptom of interference is often reduced sensitivity rather than false alarms, which is why periodic live-tag testing is essential.

Supermarkets, pharmacies, hardware and any store with wide entrances, metallic stock or high-value items where detection reliability outweighs tag cost.

Grocery is the classic case: wide doors, foil and tinned goods, bottles, and a mixture of source-tagged and store-tagged items.

Pharmacy and health and beauty suit it for the same reasons at smaller scale, with high value per unit justifying the tag cost.

Apparel retailers frequently use it with reusable hard tags, where the tag cost is amortised over many uses.

Stores tagging enormous volumes of low-value packaged goods usually find radio frequency more economic.

The supply chain can decide it: if suppliers source-tag with one technology, the store is largely committed to matching it.

Yes, but each needs its own antennas and its own till-side process, which doubles the operational load.

The technologies do not interoperate. An acoustomagnetic pedestal does not detect a radio-frequency label and vice versa.

Dual-technology pedestals exist that house both systems in one housing, which solves the entrance but not the till.

At the counter, both a deactivation method for each label type and detachers for each tag family are needed, and operators must apply the right one.

That complexity is why most stores standardise, and why a mixed estate usually reflects an incomplete migration rather than a deliberate design.

Where a mix is unavoidable - typically because of source-tagged supplier stock - document which product groups use which, and audit the till process.