The multitool now properly releases its buffer reference when the buffer is destroyed.

code/datums/expansions/multitool/circuitboards/stationalert.dm

@@ -1,6 +1,6 @@
 /datum/expansion/multitool/circuitboards/stationalert/get_interact_window(var/obj/item/device/multitool/M, var/mob/user)
 	var/obj/item/weapon/circuitboard/stationalert/SA = holder
-	. += "<b>Alarm Sources<b><br>"
+	. += "<b>Alarm Sources</b><br>"
 	. += "<table>"
 	for(var/datum/alarm_handler/AH in alarm_manager.all_handlers)
 		. += "<tr>"

code/game/machinery/computer/station_alert.dm

@@ -27,14 +27,14 @@
 	. = ..()
 	unregister()
 
-/obj/machinery/computer/station_alert/proc/register(var/datum/nano_module/alarm_monitor/monitor)
+/obj/machinery/computer/station_alert/proc/register_monitor(var/datum/nano_module/alarm_monitor/monitor)
 	if(monitor.host != src)
 		return
 
 	alarm_monitor = monitor
 	alarm_monitor.register(src, /obj/machinery/computer/station_alert/update_icon)
 
-/obj/machinery/computer/station_alert/proc/unregister()
+/obj/machinery/computer/station_alert/proc/unregister_monitor()
 	if(alarm_monitor)
 		alarm_monitor.unregister(src)
 		qdel(alarm_monitor)

code/game/objects/items/devices/multitool.dm

@@ -32,8 +32,19 @@
 
 /obj/item/device/multitool/proc/set_buffer(var/atom/buffer)
 	if(!buffer || istype(buffer))
-		buffer_object = buffer
 		buffer_name = buffer ? buffer.name : null
+		if(buffer != buffer_object)
+			if(buffer_object)
+				buffer_object.unregister(OBSERVER_EVENT_DESTROY, src)
+			buffer_object = buffer
+			if(buffer_object)
+				buffer_object.register(OBSERVER_EVENT_DESTROY, src, /obj/item/device/multitool/proc/on_buffer_destroyed)
+
+/obj/item/device/multitool/proc/on_buffer_destroyed(var/atom/destroyed_buffer)
+	// Only remove the buffered object, don't reset the name
+	// This means one cannot know if the buffer has been destroyed until one attempts to use it.
+	if(destroyed_buffer == buffer_object)
+		buffer_object = null
 
 /obj/item/device/multitool/resolve_attackby(atom/A, mob/user)
 	if(!isobj(A))

code/game/objects/items/weapons/circuitboards/computer/station_alert.dm

@@ -10,14 +10,14 @@
 
 /obj/item/weapon/circuitboard/stationalert/construct(var/obj/machinery/computer/station_alert/SA)
 	if(..(SA))
-		SA.unregister()
+		SA.unregister_monitor()
 
 		var/datum/nano_module/alarm_monitor/monitor = new(SA)
 		monitor.alarm_handlers.Cut()
 		for(var/alarm_handler in alarm_handlers)
 			monitor.alarm_handlers += alarm_handler
 
-		SA.register(monitor)
+		SA.register_monitor(monitor)
 		return 1
 
 /obj/item/weapon/circuitboard/stationalert/deconstruct(var/obj/machinery/computer/station_alert/SA)