  Information encoding in barcodes using magnetic-based technology is a unique
strategy to read data buried underneath non-transparent surfaces since a direct
line-of-sight between the code and the reader is not required. This technology
is of particular interest in secure labelling and recyclable packaging
applications. However, current magnetic reading heads, such as those employed
for magnetic ink character recognition, need to be placed in contact with the
magnetic structures, limiting the depths at which the information can be read.
This paper describes a strategy to overcome that limitation by replacing the
traditional inductive heads with tunnel magnetoresistive (TMR) sensors.
Soft-magnetic codes can be printed using conventional LaserJet toners and, by
having their magnetisation set with a permanent magnet included in the device,
the resulting magnetic field can be read using a TMR sensor. We demonstrate
that such a device can read barcodes at depths of at least 1 mm. It can also
resolve individual structures as thin as 200 {\mu}m when used in contact.
