Tone locking is simply a module used by RepeaterBook.com to prevent the release of the Uplink and Downlink tones associated with a repeater. This is only done at the request of a repeater owner.

It is believed that this is primarily requested as a method to limit access to a repeater and afford privacy on a closed or private repeater.

However, most modern amateur radios include a tone scan function and modern scanners can locate a tone in less than a second. If all else fails, a user could simply try each tone until one successfully activated the repeater. This is a poor attempt at limiting access to a repeater that beacons its existence every time it is used.