diff --git a/sections/new-hooks.md b/sections/new-hooks.md
index 587ccfd5..99c56380 100644
--- a/sections/new-hooks.md
+++ b/sections/new-hooks.md
@@ -93,6 +93,9 @@ For example:
     types: [text]
 ```
 
+To determine if an application was spawned as a `pre-commit` hook you can check
+for the existence of the `PRE_COMMIT` environment variable.
+
 ## Developing hooks interactively
 
 Since the [`repo`](#repos-repo) property of `.pre-commit-config.yaml` can refer to anything