Adds a cover lock for fire alarms, makes fire alarms trip the lock when a fire is encountered

code/game/machinery/firealarm.dm

@@ -28,6 +28,7 @@
 	resistance_flags = FIRE_PROOF
 	layer = ABOVE_WINDOW_LAYER
 	zmm_flags = ZMM_MANGLE_PLANES
+	req_access = null
 
 	light_power = 0
 	light_range = 7
@@ -37,9 +38,12 @@
 	var/buildstage = 2 // 2 = complete, 1 = no wires, 0 = circuit gone
 	var/last_alarm = 0
 	var/area/myarea = null
+	var/locked = FALSE //Are we locked?
 
 /obj/machinery/firealarm/Initialize(mapload, dir, building)
 	. = ..()
+	if (!req_access)
+		req_access = list(ACCESS_ATMOSPHERICS)
 	if(building)
 		buildstage = 0
 		panel_open = TRUE
@@ -118,6 +122,7 @@
 /obj/machinery/firealarm/temperature_expose(datum/gas_mixture/air, temperature, volume)
 	if((temperature > T0C + 200 || temperature < BODYTEMP_COLD_DAMAGE_LIMIT) && (last_alarm+FIREALARM_COOLDOWN < world.time) && !(obj_flags & EMAGGED) && detecting && !machine_stat)
 		alarm()
+		try_lock(null, TRUE)
 	..()
 
 /obj/machinery/firealarm/proc/alarm(mob/user)
@@ -138,13 +143,33 @@
 	if(user)
 		log_game("[user] reset a fire alarm at [COORD(src)]")
 
+/obj/machinery/firealarm/proc/try_lock(mob/user, force_lock = FALSE)
+	if(allowed(user) || !user || force_lock)
+		if(!locked || force_lock)
+			locked = TRUE
+			balloon_alert(user, "Locked")
+		else
+			locked = FALSE
+			balloon_alert(user, "Unlocked")
+		playsound(src, 'sound/machines/beep.ogg', 50, 1)
+	else
+		balloon_alert(user, "Access Denied!")
+		playsound(src, 'sound/machines/terminal_error.ogg', 50, 1)
+
+/obj/machinery/firealarm/AltClick(mob/user)
+	try_lock(user)
+
 /obj/machinery/firealarm/attack_hand(mob/user)
 	if(buildstage != 2)
 		return ..()
 	add_fingerprint(user)
 	play_click_sound("button")
 	var/area/A = get_area(src)
 	if(A.fire)
+		if(locked)
+			balloon_alert(user, "Cover is locked!")
+			playsound(loc, 'sound/effects/glassknock.ogg', 10, FALSE, frequency = 32000)
+			return
 		reset(user)
 	else
 		alarm(user)