ERC notifications on channels where there was activity after some inactivity

I need to monitor few IRC channels and I use Emacs so I write simple elisp function that I append to erc-insert-pre-hook and it notify me when there is some activity on those channels. I made this mainly because I what to know if someone visit #openclipart channel (because people where visiting ask question and leave after few minutes, there is no much activity on this channel)

(setq inactivity-buffer-alist '(("#openclipart" (inactivity . 900))
                                ("#hackerrank" (inactivity . 900))
                                ("#aiki" (inactivity . 900))))

(defun channel-activity (string &rest ignore)
  "notification when there is activity on a erc channel after inactivity"
  (let* ((buffer (buffer-name))
         (buffer-alist-pair (assoc buffer inactivity-buffer-alist))
         (buffer-alist (cdr buffer-alist-pair))
         (current-time (current-time)))
    (if (not (null buffer-alist))
        (let ((last-time-pair (assoc 'last-time buffer-alist))
              (inactivity (cdr (assoc 'inactivity buffer-alist))))
          (if (not (and (string-match "^\\*\\*\\*" string)
                        (string-match "[freenode-info]" string)))
              (progn
                (if (or (null last-time-pair)
                        (> (float-time (time-subtract current-time
                                                      (cdr last-time-pair)))
                           inactivity))
                    (async-exec-command "mpg123 -q /home/kuba/Pobrane/beep-6.mp3"))
                (if (null last-time-pair)
                    (setf (cdr buffer-alist-pair)
                          (append buffer-alist
                                  (list (cons 'last-time current-time))))
                  (setf (cdr last-time-pair) current-time))))))))

(add-hook 'erc-insert-pre-hook 'channel-activity)

You can add your channels to inactivity-buffer-alist along with time of inactivity (in miliseconds)

The function I use for notification is play sound using (async-exec-command "mpg123 -q /home/kuba/Pobrane/beep-6.mp3") – normal shell command was stoping execution of Emacs for few seconds

The code for this function is as follow

(defun async-exec-command (command &rest success)
  (interactive)
  (let* ((buffer-name (generate-new-buffer-name "**shell**"))
         (buffer (get-buffer-create buffer-name))
         (process (apply #'start-process
                         (append (list buffer-name buffer)
                                 (split-string command " ")))))
    (lexical-let ((buffer buffer) (success (car success)) (command command))
      (set-process-sentinel process
                            (if success (lambda (process str)
                                          (if (string= str "finished\n")
                                              (save-excursion
                                                (set-buffer buffer)
                                                (let ((content (buffer-string)))
                                                  (kill-buffer buffer)
                                                  (funcall success content)))))
                              (lambda (proces str)
                                (kill-buffer buffer)))))
    (concat "execute: " command)))