Pet microchips operate at one of three low frequencies: 125 kHz, 128 kHz, or 134.2 kHz. That is the entire list. A scanner that does not read the frequency of the chip in front of it will report “no chip found” — not because there is no chip, but because it cannot hear it.
That single sentence is why frequency matters to anyone who isn’t an engineer, and it is the reason universal scanners exist.
The three frequencies
| Frequency | Standard | Where you find it |
|---|---|---|
| 125 kHz | Non-ISO | The predominant frequency implanted in the United States |
| 128 kHz | Non-ISO | Introduced later, US market |
| 134.2 kHz | ISO 11784 / 11785 | The international standard — Canada, Europe, Asia, Australia |
All three are low frequency. Pet microchips do not use high frequency (13.56 MHz) or ultra-high frequency (860–960 MHz) — those are warehouse inventory and livestock ear-tag technologies. Low frequency is used for implants because it passes through tissue and water, which higher frequencies do not do well.
The United States is the outlier
This is the part that gets stated backwards constantly. 134.2 kHz is the world standard. ISO 11784 and 11785 were implemented in 1996 and are accepted across Canada, Europe, Asia and Australia.
The United States never moved. The AVMA describes 125 kHz non-ISO chips as remaining the predominant frequency implanted in the US, with 128 kHz and ISO 134.2 kHz introduced alongside rather than replacing it. The result is a country running three incompatible frequencies at once while the rest of the world runs one.
So a pet chipped abroad and brought to the US, or chipped here and taken abroad, can easily meet a scanner that cannot read it.
Will a scanner read my pet’s chip?
This is what people actually want to know, so here it is directly.
- A single-frequency scanner reads one frequency. Point it at a chip on a different frequency and it returns nothing at all. It does not tell you it is the wrong tool — it tells you there is no chip.
- A universal (forward- and backward-reading) scanner reads all three. That is the only kind that cannot produce a false negative on frequency grounds.
- You cannot tell which kind a clinic has by looking. They look the same. The only way to know is to ask whether it reads 125, 128 and 134.2 kHz.
If your pet is scanned and comes back as unchipped — and you know it is chipped — the first question is not whether the chip failed. It is what scanner was used. Ask them to try again with a universal scanner before you accept the result.
What frequency has nothing to do with
Frequency determines whether a chip can be read. It has no bearing on whether the number, once read, leads anywhere.
A perfectly readable ISO chip on the correct frequency still returns nothing useful if the registry record behind it was never completed, or was never updated after a move. Frequency is the first failure point. Registration is the second, and it is by far the more common one.
Look your pet’s number up here and see what it actually returns.
Common questions
What frequency are pet microchips in the United States?
125 kHz, 128 kHz and 134.2 kHz are all in use. 125 kHz non-ISO is the predominant frequency implanted in the US; 134.2 kHz is the ISO international standard.
What is an ISO microchip?
A chip conforming to ISO 11784 and 11785, operating at 134.2 kHz with a 15-digit number. It is the standard required for pet travel to most countries.
Can one scanner read every pet microchip?
A universal scanner that reads 125, 128 and 134.2 kHz can read any chip on those frequencies. A single-frequency scanner cannot, and it reports a chip it cannot hear as no chip at all.
Do pet microchips use WiFi, Bluetooth or GPS?
No. A microchip is passive — it has no battery and transmits nothing on its own. It responds only when a scanner powers it from a few inches away. It cannot be tracked and no phone can read one.
Related from Peeva
- Universal microchip scanners
- ISO-compliant microchips
- How to scan a pet’s microchip
- Look up a microchip number
- Register your pet’s microchip
Frequency standards and US adoption per the American Veterinary Medical Association, Microchipping of Animals.
Microchip resources
Find the registry by microchip prefix · Look up a microchip number · Universal microchip scanners · Register your pet’s microchip
