Magnetic stripe key cards: HiCo, LoCo, and why the card stopped working

The magnetic stripe is the technology everyone expected to have disappeared by now. It has not, and it will not for years, because a working lock is a paid-for lock and a property replaces those on a capital cycle rather than a news cycle.

So the stripe remains a live procurement question in hospitality, and it is one where a small specification error produces a very visible operational failure: a guest at a door at eleven at night with a card that does nothing. Almost every one of those failures traces back to one of four things, and all four are decided before the card is manufactured.

This guide covers coercivity, tracks, placement and wear, what each one means in practice, and how to specify a stripe so that the batch behaves.

01. Coercivity, in plain terms

Coercivity is a measure of how hard it is to change the magnetic information on the stripe. It is expressed in oersteds, written Oe, and in practice the industry uses two families.

Low coercivity

Commonly around 300 Oe. The stripe is easy to write, which historically meant cheaper and faster encoders. It is also easier to erase, whether deliberately or by accident. Low coercivity stripes are traditionally brown.

High coercivity

Commonly around 2750 Oe, with some variants around 4000 Oe. Harder to write, requiring an encoder capable of producing a stronger field, and correspondingly harder to erase. High coercivity stripes are traditionally black, though colour is a convention rather than a guarantee and should never be used as the sole means of identification.

The trade-off is exactly what it sounds like. Low coercivity is easier on the encoder and more vulnerable in a pocket. High coercivity survives the world better and demands more of the equipment writing it.

Coercivity is a matched pair, not a preference.

The stripe and the encoder have to agree. A high coercivity card written by an encoder set for low coercivity receives a weak, incomplete write that may read once and then fail. A low coercivity card written at high coercivity can be over-written and distorted. Both produce cards that fail in the field rather than at the desk.

This is the single most common magnetic stripe fault, and it is the easiest to prevent. The encoder setting and the card specification must be confirmed together, not separately.

02. Tracks: three lanes, different rules

A magnetic stripe is not one continuous field of data. It is up to three parallel tracks, standardised under ISO 7811, and each has its own character set and density.

Track 1 holds alphanumeric data at higher density. It is the track that can carry letters, which historically made it useful for names.

Track 2 holds numeric data. It is the most widely used track in access control and the one most hotel systems rely on.

Track 3 is numeric and was designed to be rewritable in use. Some systems use it, many do not.

What matters for procurement is simple: the card must carry a stripe capable of holding the tracks your system writes, and the system's requirement is a fact to be established rather than a choice to be made. A card supplied with a stripe that does not support the track in use will appear to encode and will not open a door.

03. Placement, and why artwork has to yield

The stripe must sit within a defined position and tolerance so that the read head passes over it correctly. This is not a design decision. A stripe that sits a millimetre out of position produces intermittent reads that look, to a front desk, exactly like a dead card.

Two practical consequences follow.

The first is that the stripe face of the card has a reserved zone that artwork cannot occupy, and any design that ignores this will either be rejected at prepress or produce a card that fails in service. Designers who have not worked on cards before are frequently surprised by how much of that face is spoken for.

The second is that placement tolerance is a manufacturing quality question worth asking about explicitly. A supplier running a controlled process holds placement within a stated tolerance across an entire run. A supplier who does not will deliver a batch in which most cards work and a percentage do not, which is operationally worse than a batch that fails outright, because it is much harder to diagnose.

04. What actually erases a stripe

There is a great deal of folklore here, and some of it is now out of date in a way that matters.

Mobile phones: mostly myth, with a real exception

The belief that a phone erases a hotel key card dates from an era of different hardware. A phone's speaker and internal components produce a field that is generally too weak and too distant to erase a stripe through a wallet.

The genuine exception is the magnet array. Phone cases, wallets and accessory mounts built around strong magnetic attachment systems are a different proposition entirely, and a card held directly against one of those for a period can absolutely be affected. So can the magnetic clasp on a handbag, which is one of the most common real-world causes and one that almost nobody suspects.

Other cards, and everyday objects

Magnetic closures, speaker magnets, some tools, and in a hotel context the underside of certain fixtures and fittings. The common factor is proximity and strength, not exoticism.

Abrasion, which is the quiet one

A stripe wears. Every swipe abrades it slightly, and so does every journey in a pocket alongside coins and keys. A card that has been in circulation for months will eventually fail from physical wear rather than from magnetic erasure. This is normal and it is a consumable cost, but it is frequently misdiagnosed as a system fault.

When a card fails, ask how old it is before you ask what erased it.

A card in its first week that fails points to specification or encoding. A card that has been in a pocket for four months and fails points to wear, and the answer is a replacement rather than an investigation.

05. Diagnosing a failure at the front desk

A short sequence separates the four causes quickly.

Re-encode the same card. If it now works, the original encode failed or the stripe was erased. If it still fails, the card is worn or out of specification.

Try a card from a different batch. If the other batch works and this one does not, the problem is in the delivery, not the estate.

Try the failing card at a different door. Consistent failure everywhere points to the card. Failure at one door only points at the reader, which may simply need cleaning.

Check the encoder setting against the card specification. If a batch started failing after new stock arrived, this is where the answer usually is.

That sequence takes two minutes and resolves the large majority of cases without a service call.

06. Specifying a stripe order

A specification that prevents arguments contains:

• Coercivity, stated in oersteds, confirmed against the encoder rather than assumed from the colour of the stripe
• Track requirement, confirmed from the system documentation or the integrator
• Stripe placement tolerance, stated as a figure the supplier commits to
• Card body: material, thickness and finish, with thickness particularly relevant because the stripe rides on it
• Finish on the stripe face, since some finishes affect how cleanly the card passes through a reader
• Artwork, with the reserved stripe zone respected at design stage rather than at prepress

The first two are the ones that cause the failures. The rest are the ones that determine how long the card lasts.

07. When to stop buying stripe

At some point the stripe stops being a sensible purchase, and the signal is usually commercial rather than technical.

Replacement rates are the number to watch. If a property is replacing cards at a rate that has been climbing year on year, the cost is no longer just plastic. It is front desk time, guest complaints and the occasional compensated night. That total is often larger than anyone has calculated, because it sits in three different budget lines and nobody has added it up.

The second signal is security. A magnetic stripe carries no cryptography. In an estate where that has been raised in an audit or by an insurer, the conversation has already moved past cost.

The third is a mobile key programme, which is generally incompatible with keeping the stripe as the primary credential.

None of this makes the stripe wrong today. It makes it a technology with a defined remaining life, and the useful discipline is to know roughly what that life is at each property so that orders are sized to it.

08. What the stripe cannot do

Everything above concerns making a magnetic stripe work. It is worth being equally clear about what it does not do, because the gap is frequently misunderstood by people making decisions about it.

A magnetic stripe carries data in the clear. There is no cryptography, no mutual authentication between card and lock, and no mechanism by which a lock can distinguish an original card from a copy of it. The data on the stripe is a pattern of magnetic flux reversals, and reproducing that pattern requires equipment that is neither rare nor expensive.

This is not a defect in any particular product. It is the technology. It was designed in an era with different threat assumptions and it has been doing its job for decades, but the job it does is identification, not security.

Three consequences are worth stating for anyone specifying.

A lost card is a live credential until it is cancelled in the system. That is true of contactless credentials too, but the stripe adds no barrier of its own in the interval.

Duplication leaves no trace on the card. A copied stripe is indistinguishable from the original at the reader, so an audit trail records the credential, not which physical card presented it.

The exposure sits with the property, not the card supplier. When this surfaces, it usually surfaces through an insurer, an audit, or a brand standard from a franchisor, and it arrives as a deadline rather than a discussion.

None of this means the stripe should be ripped out tomorrow. It means the remaining life of a stripe estate is set by risk appetite and by whoever writes the brand standards, and that those are the parties worth asking rather than the maintenance budget.

The stripe identifies, it does not authenticate.

Everything above is about making it work reliably. None of it makes it secure, and no card specification can, because the limitation is in the technology rather than in the product.

09. Frequently asked questions

Is a black stripe always high coercivity?

It is the convention and it is usually true, but it is not a specification. Confirm the coercivity figure in writing rather than reading it off the colour.

Can we encode high coercivity cards on our existing encoder?

Only if the encoder is capable of high coercivity output. Many are, and many older units are not, or have a setting that has to be changed. Check before ordering, not after delivery.

Can a card carry both a stripe and a chip?

Yes. Hybrid cards are routine and are the usual answer for a property part-way through a migration. They cost more than either technology alone and they constrain the artwork on the stripe face.

How long should a magnetic stripe card last in a hotel?

It depends on card body quality and on how the card is carried, far more than on the stripe itself. Thickness, material and lamination determine whether a card survives months of pockets and readers, and that is where the specification is worth spending on.