Recommendation ITU-T H.870 describes the requirements on safe listening devices and systems, called personal/portable audio systems, especially those for playing music, to protect people from hearing loss. It also gives a glossary for common understanding as well as background information on sound, hearing and hearing loss.

It recommends the criteria for avoiding unsafe listening: one for adults and the other for children, both based on the equal energy principle, the assumption that equal amounts of sound energy will cause equal amounts of sound induced permanent threshold shift regardless of the distribution of the energy over time.

Importantly, this Recommendation provides guidelines on health communication for safe listening so that appropriate warning messages can be delivered effectively when necessary. Examples of such messages can be found in Appendix VII.

Finally, this Recommendation also gives information about the implementation of dosimetry and related issues.

Communication devices and assistive devices are excluded from the scope of this Recommendation. Gaming devices are also for future study.

This standard was developed collaboratively by the World Health Organization (WHO) and ITU under the 'Make Listening Safe' initiative, and it is adopted by both organizations.