A shruti box (or sruti box) is a small wooden instrument that traditionally works on a system of bellows. It is similar to a harmonium and is used to provide a drone in a practice session or concert of Indian classical music. It is used as an accompaniment to other instruments and notably the flute. Use of the shruti box has widened with the cross-cultural influences of world music and new age music to provide a drone for many other instruments as well as vocalists.

Adjustable buttons allow tuning. Nowadays, electronic shruti boxes are commonly used, which are called shruti petti in Tamil and Telugu and sur peti in Hindi.

Before the arrival of the harmonium in India, musicians used either a tambura or a specific pitch reference instrument, such as the nadaswaram, to produce the drone. Some forms of music such as Yakshagana used Pungi of the snake charmers as drone. After the harmonium became popular, musicians would modify the harmonium to automatically produce the reference pitch. Typically, one would open up the cover and adjust the stop of the harmonium to produce a drone.