CRISPR-Cas9 technology is constantly evolving. Variants of Cas9 can be used for genome editing, activating gene expression, repressing gene expression, and much more. But there’s one thing that’s been missing: a way to shut off Cas9’s activity after it’s been turned on. The concern is that the longer Cas9 remains active in a cell, the greater chances there are for off-target edits to occur. Although methods to switch on Cas9 activity using light or drugs have been developed, the field lacked an “off-switch” for Cas9.