How tap to pay works when there is no battery

Written by the Drop team

The first question almost everyone asks about a Drop Band is not about money. It is about charging.

People hear wearable and they think of a thing that dies at 4pm. They ask how long the band lasts, where the charger goes, what happens on a camping trip. The answer is that there is no charger, the band never dies, and it will work the day it arrives and every day after that.

That sounds like marketing. It is actually just physics, and the physics is worth understanding, because it explains what the band can do and, more usefully, what it cannot.

The chip has no power of its own

Inside a Drop Band there is a passive NFC chip. Passive is the important word. It means the chip has no battery, no power source, and no ability to do anything at all on its own. Sitting on your wrist, it is inert. It is closer to a printed page than to a phone.

What wakes it up is the reader.

Every contactless payment terminal, and every phone with NFC turned on, generates a small electromagnetic field a few centimeters across. When you bring the band into that field, the field induces a current in a tiny antenna coiled inside the band. That current is enough to power the chip for a fraction of a second. Long enough to run a calculation and answer.

Then you move your wrist away, the field is gone, and the chip goes dead again.

This is not a Drop invention. It is how the contactless card in your wallet works, and it is why that card also has no battery. The reader powers the card. The card is just along for the ride.

What the chip actually says

Here is where people assume wrong. They picture their card number sitting on the band, waiting to be read by anyone with the right gadget.

That is not what is stored, because nothing personal is stored on the band at all.

The band carries a pointer. When a terminal powers the chip, the chip does not recite a card number. It runs a one time cryptographic calculation and hands back a token, along with a cryptogram that is different on every single tap. The terminal passes that to the network. The network resolves it against the real account. The real account lives with the issuer, not on your wrist.

Drop Pay accounts are issued by Pathward®, N.A., Member FDIC, with verified KYC and AML checks at account opening. Tokenized EMV, with a fresh cryptogram for every tap.

If someone copied the exact data from one tap, they would have a cryptogram that has already been used. The next tap needs a different one. This is the same standard protecting the contactless card already in your pocket.

Why this is the reason there is no tracking

The interesting part of a passive chip is not what it does. It is what it structurally cannot do.

A device that tracks you needs power all day. GPS needs power. Bluetooth needs power. A microphone needs power. Anything that reports where you are, continuously, needs a battery, and the moment you add a battery you have added a thing that must be charged, a thing that dies, and a thing that is listening when nobody asked it to.

A Drop Band has no battery. So it has no GPS, no Bluetooth and no microphone. Not as a feature we chose to leave out of version one. As a consequence of the design.

The band is active for the instant it touches a reader and dead the rest of the day. It cannot report your location because it has no power to report anything, and no radio to report it with, and nowhere to send it.

We should be straight about the trade. If what your family needs is the ability to see where your kid is on a map, buy a tracker. That is a real need and Drop deliberately does not meet it. What Drop offers instead is a kid who can identify themselves, carry emergency information, get into the places they belong, and pay for lunch, without carrying a screen and without being followed.

What no battery changes day to day

• Nothing to charge, ever. No cable, no dock, no dead band at a sleepover.
• Water is not an event. The band is water resistant elastic fabric, 14mm wide.
• No battery to swell, degrade or age out after two years.
• It works on day one and it works identically on day four hundred.
• Nothing to remember. It is on your wrist, so it is with you.

And what it does not change

The band still needs the Drop app. The band has no screen and no settings of its own, which means every decision about what it can do gets made by a person, on a phone, deliberately. Identity, connections, what is on, and spending. That is not a limitation of the hardware. It is the point of it.

Questions people ask

Does the Drop Band ever need charging?

Never. There is no battery and no screen. The chip inside is passive, powered for a fraction of a second by the reader it touches, then dead again. It works the day it arrives and every day after.

Can someone steal money by scanning my band?

No. The band holds no card number. Each tap produces a one time token and a fresh cryptogram, so captured data cannot be replayed. If the band is lost, open the Drop app and turn it off in one tap.

Does the band track location?

No. The band has no GPS, no Bluetooth and no microphone. A passive chip has no power to run them. Families who specifically want location tracking should buy a tracker, because Drop is not one.

Is this different from a contactless card?

The mechanism is the same tokenized EMV standard your contactless card uses. The difference is form and control. The band is on a wrist instead of in a wallet, and every setting lives in the Drop app rather than with the card.