diff --git a/cmd-attach-session.c b/cmd-attach-session.c
index 9f357d6e..356bd4aa 100644
--- a/cmd-attach-session.c
+++ b/cmd-attach-session.c
@@ -135,7 +135,7 @@ cmd_attach_session(struct cmd_q *cmdq, const char *tflag, int dflag, int rflag,
 		c->session = s;
 		status_timer_start(c);
 		notify_attached_session_changed(c);
-		session_update_activity(s);
+		session_update_activity(s, NULL);
 		server_redraw_client(c);
 		s->curw->flags &= ~WINLINK_ALERTFLAGS;
 	} else {
@@ -180,7 +180,7 @@ cmd_attach_session(struct cmd_q *cmdq, const char *tflag, int dflag, int rflag,
 		c->session = s;
 		status_timer_start(c);
 		notify_attached_session_changed(c);
-		session_update_activity(s);
+		session_update_activity(s, NULL);
 		server_redraw_client(c);
 		s->curw->flags &= ~WINLINK_ALERTFLAGS;
 
diff --git a/cmd-new-session.c b/cmd-new-session.c
index 2125ee88..fa4f1553 100644
--- a/cmd-new-session.c
+++ b/cmd-new-session.c
@@ -277,7 +277,7 @@ cmd_new_session_exec(struct cmd *self, struct cmd_q *cmdq)
 		c->session = s;
 		status_timer_start(c);
 		notify_attached_session_changed(c);
-		session_update_activity(s);
+		session_update_activity(s, NULL);
 		server_redraw_client(c);
 	}
 	recalculate_sizes();
diff --git a/cmd-set-option.c b/cmd-set-option.c
index 260961cb..56ca91e0 100644
--- a/cmd-set-option.c
+++ b/cmd-set-option.c
@@ -176,7 +176,7 @@ cmd_set_option_exec(struct cmd *self, struct cmd_q *cmdq)
 			return (CMD_RETURN_ERROR);
 	}
 
-	/* Start or stop timers when name or status options changed. */
+	/* Start or stop timers if necessary. */
 	if (strcmp(oe->name, "automatic-rename") == 0) {
 		RB_FOREACH(w, windows, &windows) {
 			if (options_get_number(&w->options, "automatic-rename"))
diff --git a/cmd-switch-client.c b/cmd-switch-client.c
index 6a79c7b7..8bc8a3c5 100644
--- a/cmd-switch-client.c
+++ b/cmd-switch-client.c
@@ -128,7 +128,7 @@ cmd_switch_client_exec(struct cmd *self, struct cmd_q *cmdq)
 		c->last_session = c->session;
 	c->session = s;
 	status_timer_start(c);
-	session_update_activity(s);
+	session_update_activity(s, NULL);
 
 	recalculate_sizes();
 	server_check_unattached();
diff --git a/names.c b/names.c
index 0a3af903..aa0673ea 100644
--- a/names.c
+++ b/names.c
@@ -50,10 +50,6 @@ window_name_callback(unused int fd, unused short events, void *data)
 	if (w->active == NULL)
 		return;
 
-	if (~w->active->flags & PANE_CHANGED)
-		return;
-	w->active->flags &= ~PANE_CHANGED;
-
 	if (!options_get_number(&w->options, "automatic-rename")) {
 		if (event_initialized(&w->name_timer))
 			event_del(&w->name_timer);
@@ -61,6 +57,10 @@ window_name_callback(unused int fd, unused short events, void *data)
 	}
 	queue_window_name(w);
 
+	if (~w->active->flags & PANE_CHANGED)
+		return;
+	w->active->flags &= ~PANE_CHANGED;
+
 	name = format_window_name(w);
 	if (strcmp(name, w->name) != 0) {
 		window_set_name(w, name);
diff --git a/server-client.c b/server-client.c
index fab1c1a0..1faf5968 100644
--- a/server-client.c
+++ b/server-client.c
@@ -560,9 +560,7 @@ server_client_handle_key(struct client *c, int key)
 	/* Update the activity timer. */
 	if (gettimeofday(&c->activity_time, NULL) != 0)
 		fatal("gettimeofday failed");
-	memcpy(&s->last_activity_time, &s->activity_time,
-	    sizeof s->last_activity_time);
-	memcpy(&s->activity_time, &c->activity_time, sizeof s->activity_time);
+	session_update_activity(s, &c->activity_time);
 
 	/* Number keys jump to pane in identify mode. */
 	if (c->flags & CLIENT_IDENTIFY && key >= '0' && key <= '9') {
@@ -990,6 +988,7 @@ server_client_msg_dispatch(struct client *c)
 	struct msg_stdin_data	 stdindata;
 	const char		*data;
 	ssize_t			 n, datalen;
+	struct session		*s;
 
 	if ((n = imsg_read(&c->ibuf)) == -1 || n == 0)
 		return (-1);
@@ -1073,11 +1072,12 @@ server_client_msg_dispatch(struct client *c)
 
 			if (c->tty.fd == -1) /* exited in the meantime */
 				break;
+			s = c->session;
 
 			if (gettimeofday(&c->activity_time, NULL) != 0)
 				fatal("gettimeofday");
-			if (c->session != NULL)
-				session_update_activity(c->session);
+			if (s != NULL)
+				session_update_activity(s, &c->activity_time);
 
 			tty_start_tty(&c->tty);
 			server_redraw_client(c);
diff --git a/server-fn.c b/server-fn.c
index b7ff9443..076e4e72 100644
--- a/server-fn.c
+++ b/server-fn.c
@@ -424,7 +424,7 @@ server_destroy_session(struct session *s)
 			c->session = s_new;
 			status_timer_start(c);
 			notify_attached_session_changed(c);
-			session_update_activity(s_new);
+			session_update_activity(s_new, NULL);
 			server_redraw_client(c);
 		}
 	}
diff --git a/server.c b/server.c
index 3916cd7a..62d05ebe 100644
--- a/server.c
+++ b/server.c
@@ -45,7 +45,6 @@ struct clients	 clients;
 int		 server_fd;
 int		 server_shutdown;
 struct event	 server_ev_accept;
-struct event	 server_ev_second;
 
 struct session		*marked_session;
 struct winlink		*marked_winlink;
@@ -62,8 +61,6 @@ void	server_signal_callback(int, short, void *);
 void	server_child_signal(void);
 void	server_child_exited(pid_t, int);
 void	server_child_stopped(pid_t, int);
-void	server_second_callback(int, short, void *);
-void	server_lock_sessions(void);
 
 /* Set marked pane. */
 void
@@ -162,9 +159,8 @@ server_create_socket(void)
 int
 server_start(int lockfd, char *lockfile)
 {
-	int	 	 pair[2];
-	struct timeval	 tv;
-	char		*cause;
+	int	 pair[2];
+	char	*cause;
 
 	/* The first client is special and gets a socketpair; create it. */
 	if (socketpair(AF_UNIX, SOCK_STREAM, PF_UNSPEC, pair) != 0)
@@ -244,11 +240,6 @@ server_start(int lockfd, char *lockfile)
 
 	server_add_accept(0);
 
-	memset(&tv, 0, sizeof tv);
-	tv.tv_sec = 1;
-	evtimer_set(&server_ev_second, server_second_callback, NULL);
-	evtimer_add(&server_ev_second, &tv);
-
 	set_signals(server_signal_callback);
 	server_loop();
 	status_prompt_save_history();
@@ -499,37 +490,3 @@ server_child_stopped(pid_t pid, int status)
 		}
 	}
 }
-
-/* Handle once-per-second timer events. */
-void
-server_second_callback(unused int fd, unused short events, unused void *arg)
-{
-	struct timeval		 tv;
-
-	server_lock_sessions();
-
-	evtimer_del(&server_ev_second);
-	memset(&tv, 0, sizeof tv);
-	tv.tv_sec = 1;
-	evtimer_add(&server_ev_second, &tv);
-}
-
-/* Lock any sessions which have timed out. */
-void
-server_lock_sessions(void)
-{
-	struct session  *s;
-	int		 timeout;
-	time_t		 t;
-
-	t = time(NULL);
-	RB_FOREACH(s, sessions, &sessions) {
-		if (s->flags & SESSION_UNATTACHED)
-			continue;
-		timeout = options_get_number(&s->options, "lock-after-time");
-		if (timeout > 0 && t > s->activity_time.tv_sec + timeout) {
-			server_lock_session(s);
-			recalculate_sizes();
-		}
-	}
-}
diff --git a/session.c b/session.c
index e0d06ec9..b8472c2a 100644
--- a/session.c
+++ b/session.c
@@ -32,6 +32,8 @@ struct session_groups session_groups;
 
 void	session_free(int, short, void *);
 
+void	session_lock_timer(int, short, void *);
+
 struct winlink *session_next_alert(struct winlink *);
 struct winlink *session_previous_alert(struct winlink *);
 
@@ -107,14 +109,10 @@ session_create(const char *name, int argc, char **argv, const char *path,
 	struct session	*s;
 	struct winlink	*wl;
 
-	s = xmalloc(sizeof *s);
+	s = xcalloc(1, sizeof *s);
 	s->references = 1;
 	s->flags = 0;
 
-	if (gettimeofday(&s->creation_time, NULL) != 0)
-		fatal("gettimeofday failed");
-	session_update_activity(s);
-
 	s->cwd = dup(cwd);
 
 	s->curw = NULL;
@@ -132,6 +130,10 @@ session_create(const char *name, int argc, char **argv, const char *path,
 		memcpy(s->tio, tio, sizeof *s->tio);
 	}
 
+	if (gettimeofday(&s->creation_time, NULL) != 0)
+		fatal("gettimeofday failed");
+	session_update_activity(s, &s->creation_time);
+
 	s->sx = sx;
 	s->sy = sy;
 
@@ -148,6 +150,10 @@ session_create(const char *name, int argc, char **argv, const char *path,
 	}
 	RB_INSERT(sessions, &sessions, s);
 
+	if (gettimeofday(&s->creation_time, NULL) != 0)
+		fatal("gettimeofday failed");
+	session_update_activity(s, &s->creation_time);
+
 	if (argc >= 0) {
 		wl = session_new(s, NULL, argc, argv, path, cwd, idx, cause);
 		if (wl == NULL) {
@@ -182,8 +188,10 @@ session_free(unused int fd, unused short events, void *arg)
 
 	log_debug("sesson %s freed (%d references)", s->name, s->references);
 
-	if (s->references == 0)
+	if (s->references == 0) {
+		free(s->name);
 		free(s);
+	}
 }
 
 /* Destroy a session. */
@@ -199,6 +207,9 @@ session_destroy(struct session *s)
 
 	free(s->tio);
 
+	if (event_initialized(&s->lock_timer))
+		event_del(&s->lock_timer);
+
 	session_group_remove(s);
 	environ_free(&s->environ);
 	options_free(&s->options);
@@ -223,12 +234,46 @@ session_check_name(const char *name)
 	return (*name != '\0' && name[strcspn(name, ":.")] == '\0');
 }
 
-/* Update session active time. */
+/* Lock session if it has timed out. */
 void
-session_update_activity(struct session *s)
+session_lock_timer(unused int fd, unused short events, void *arg)
 {
-	if (gettimeofday(&s->activity_time, NULL) != 0)
-		fatal("gettimeofday");
+	struct session	*s = arg;
+
+	if (s->flags & SESSION_UNATTACHED)
+		return;
+
+	log_debug("session %s locked, activity time %lld", s->name,
+	    (long long)s->activity_time.tv_sec);
+
+	server_lock_session(s);
+	recalculate_sizes();
+}
+
+/* Update activity time. */
+void
+session_update_activity(struct session *s, struct timeval *from)
+{
+	struct timeval	*last = &s->last_activity_time;
+	struct timeval	 tv;
+
+	memcpy(last, &s->activity_time, sizeof *last);
+	if (from == NULL)
+		gettimeofday(&s->activity_time, NULL);
+	else
+		memcpy(&s->activity_time, from, sizeof s->activity_time);
+
+	if (evtimer_initialized(&s->lock_timer))
+		evtimer_del(&s->lock_timer);
+	else
+		evtimer_set(&s->lock_timer, session_lock_timer, s);
+
+	if (~s->flags & SESSION_UNATTACHED) {
+		timerclear(&tv);
+		tv.tv_sec = options_get_number(&s->options, "lock-after-time");
+		if (tv.tv_sec != 0)
+			evtimer_add(&s->lock_timer, &tv);
+	}
 }
 
 /* Find the next usable session. */
diff --git a/tmux.h b/tmux.h
index 3d77d9a0..8678794e 100644
--- a/tmux.h
+++ b/tmux.h
@@ -997,6 +997,8 @@ struct session {
 	struct timeval	 activity_time;
 	struct timeval	 last_activity_time;
 
+	struct event	 lock_timer;
+
 	u_int		 sx;
 	u_int		 sy;
 
@@ -2252,7 +2254,7 @@ struct session	*session_create(const char *, int, char **, const char *,
 void		 session_destroy(struct session *);
 void		 session_unref(struct session *);
 int		 session_check_name(const char *);
-void		 session_update_activity(struct session *);
+void		 session_update_activity(struct session *, struct timeval *);
 struct session	*session_next_session(struct session *);
 struct session	*session_previous_session(struct session *);
 struct winlink	*session_new(struct session *, const char *, int, char **,