diff --git a/elisp/chronometrist.el b/elisp/chronometrist.el
index d6e6688..07fa1a0 100644
--- a/elisp/chronometrist.el
+++ b/elisp/chronometrist.el
@@ -3519,6 +3519,39 @@ Return value is a list as specified by `tabulated-list-entries'."
     do (cl-incf index)))
 ;; rows:1 ends here
 
+;; [[file:chronometrist.org::*define-alert-system][define-alert-system:1]]
+(defmacro chronometrist-define-alert-system (extension initvalue &rest custom-args)
+  "Define an alerts system for EXTENSION.
+Defines a custom variable `chronometrist-EXTENSION-alerts-alist'
+with INITVALUE and CUSTOM-ARGS, a variable
+`chronometrist-EXTENSION--timer-list', and a procedure
+`chronometrist-EXTENSION-run-at-time'."
+  (let* ((prefix     (format "chronometrist-%s" extension))
+         (custom-var (intern (format "%s-alerts-alist" prefix)))
+         (list-var   (intern (format "%s--timer-alist" prefix)))
+         (function   (intern (format "%s-run-at-time" prefix))))
+    `(progn
+       (defcustom ,custom-var ,initvalue
+         ,(let ((docstring (format "Alist of alerts run by `%s'.
+
+Each element must be in the form (SYMBOL FUNCTION ALERT-FN &rest ALERT-ARGS),
+where SYMBOL uniquely identifies the alert,
+FUNCTION is a function calling `%s' and ALERT-FN,
+and ALERT-ARGS are passed to ALERT-FN."
+                                   prefix function)))
+            (with-temp-buffer
+              (insert docstring)
+              (fill-region (point-min) (point-max))
+              (buffer-substring-no-properties (point-min) (point-max))))
+         ,@custom-args)
+       (defvar ,list-var nil ,(format "Alist of timers created for `%s'." prefix))
+       (defun  ,function (time repeat function &rest args)
+         ,(format "Like `run-at-time', but store timer objects in `%s'." ,list-var)
+         (cl-pushnew (apply #'run-at-time time repeat function args) ,list-var)))))
+
+;; (chronometrist-define-alert-system foo nil)
+;; define-alert-system:1 ends here
+
 (provide 'chronometrist)
 
 ;;; chronometrist.el ends here
diff --git a/elisp/chronometrist.org b/elisp/chronometrist.org
index 0d9d25c..27f9c45 100644
--- a/elisp/chronometrist.org
+++ b/elisp/chronometrist.org
@@ -4757,6 +4757,41 @@ Return value is a list as specified by `tabulated-list-entries'."
     do (cl-incf index)))
 #+END_SRC
 
+** Extension utilities
+*** define-alert-system
+#+BEGIN_SRC emacs-lisp
+(defmacro chronometrist-define-alert-system (extension initvalue &rest custom-args)
+  "Define an alerts system for EXTENSION.
+Defines a custom variable `chronometrist-EXTENSION-alerts-alist'
+with INITVALUE and CUSTOM-ARGS, a variable
+`chronometrist-EXTENSION--timer-list', and a procedure
+`chronometrist-EXTENSION-run-at-time'."
+  (let* ((prefix     (format "chronometrist-%s" extension))
+         (custom-var (intern (format "%s-alerts-alist" prefix)))
+         (list-var   (intern (format "%s--timer-alist" prefix)))
+         (function   (intern (format "%s-run-at-time" prefix))))
+    `(progn
+       (defcustom ,custom-var ,initvalue
+         ,(let ((docstring (format "Alist of alerts run by `%s'.
+
+Each element must be in the form (SYMBOL FUNCTION ALERT-FN &rest ALERT-ARGS),
+where SYMBOL uniquely identifies the alert,
+FUNCTION is a function calling `%s' and ALERT-FN,
+and ALERT-ARGS are passed to ALERT-FN."
+                                   prefix function)))
+            (with-temp-buffer
+              (insert docstring)
+              (fill-region (point-min) (point-max))
+              (buffer-substring-no-properties (point-min) (point-max))))
+         ,@custom-args)
+       (defvar ,list-var nil ,(format "Alist of timers created for `%s'." prefix))
+       (defun  ,function (time repeat function &rest args)
+         ,(format "Like `run-at-time', but store timer objects in `%s'." ,list-var)
+         (cl-pushnew (apply #'run-at-time time repeat function args) ,list-var)))))
+
+;; (chronometrist-define-alert-system foo nil)
+#+END_SRC
+
 ** Provide
 #+BEGIN_SRC emacs-lisp :comments no
 (provide 'chronometrist)