Micro QR code
A compact QR variant with one finder pattern, for very small marks.
Micro QR is a reduced variant defined alongside standard QR in ISO/IEC 18004. It has one finder pattern instead of three, and comes in four sizes from M1 (11×11 modules) to M4 (17×17).
Capacity. Very small — M4 holds about 35 numeric characters or 21 alphanumeric at the lowest error correction. It suits part numbers and serials, not URLs.
Why it is rare. Scanner support is patchy. Industrial scanners handle it; consumer phone cameras frequently do not. For anything a member of the public will scan, a standard version 1 QR code is the safer choice despite being physically larger.
Where it is used. Electronics manufacturing and component marking, where the marking area is measured in millimetres and the readers are purpose-built.
In practice
A circuit board needs a serial number in a 4mm square. A standard version 1 QR code is 21×21 modules plus an 8-module quiet zone — 29 modules across, giving 0.14mm modules at that size, far below what prints or scans. An M3 Micro QR is 15 modules with a 2-module quiet zone, giving roughly 0.21mm.
Still demanding, but achievable with laser marking and an industrial reader. Which is exactly the point: Micro QR exists for controlled environments where you own the scanners, not for anything a customer will point a phone at.
Questions
Will a phone scan a Micro QR code?
Sometimes. Support is inconsistent across devices and apps, and a code that works on your phone may not work on your customers'. For public-facing use, a standard version 1 code is the safe choice.
Why is the quiet zone smaller?
Micro QR requires two modules rather than four, which is part of how it achieves a smaller overall footprint for the same marking area.