HTC One M8 for Windows - Manual (Page 13)

Important RF Notice
This device was tested for compliance with the applicable FCC and
Industry Canada specific absorption rate (SAR) limits for radio
frequency (RF) exposure during typical body-worn operations. To
ensure that RF exposure levels remain at or below the tested levels,
use a belt-clip, holster, or similar accessory that maintains a
minimum separation distance of 1.0 cm between your body and the
device, with either the front or back of the device facing towards
your body. Such accessories should not contain any metallic
components. Body-worn accessories that do not meet these
specifications may not ensure compliance with applicable SAR limits
and their use should be avoided.
Important RF Notice 13