A sensor which registers mechs and trains attempting to pass by and, if necessary, blocks their movement.

If enabled, detects mechs/trains and blocks their movement if they are coming from any of the directions set by dir. Can currently only be enabled/disabled by radio command and airlocks are updated to utilize this.

The current setup allows mechs to move through airlocks during normal cycles, which for example lets Odysseus out to save lives.
Once a shuttle docks however, the sensors are enabled to prevent boarding.

If blocked, players receive a simple message stating that their command has been overridden.

code/game/machinery/embedded_controller/airlock_controllers.dm

@@ -7,6 +7,7 @@
 	var/tag_chamber_sensor
 	var/tag_exterior_sensor
 	var/tag_interior_sensor
+	var/tag_mech_sensor
 	var/tag_secure = 0
 
 /obj/machinery/embedded_controller/radio/airlock/initialize()

code/game/machinery/embedded_controller/airlock_docking_controller.dm

@@ -99,12 +99,14 @@
 
 //we are docked, open the doors or whatever.
 /datum/computer/file/embedded_program/docking/airlock/finish_docking()
+	airlock_program.enable_mech_regulators()
 	airlock_program.open_doors()
 
 //tell the docking port to start getting ready for undocking - e.g. close those doors.
 /datum/computer/file/embedded_program/docking/airlock/prepare_for_undocking()
 	airlock_program.stop_cycling()
 	airlock_program.close_doors()
+	airlock_program.disable_mech_regulators()
 
 //are we ready for undocking?
 /datum/computer/file/embedded_program/docking/airlock/ready_for_undocking()
@@ -115,13 +117,18 @@
 //An airlock controller to be used by the airlock-based docking port controller.
 //Same as a regular airlock controller but allows disabling of the regular airlock functions when docking
 /datum/computer/file/embedded_program/airlock/docking
-	
 	var/datum/computer/file/embedded_program/docking/airlock/master_prog
 
 /datum/computer/file/embedded_program/airlock/docking/receive_user_command(command)
 	if (master_prog.undocked() || master_prog.override_enabled)	//only allow the port to be used as an airlock if nothing is docked here or the override is enabled
 		..(command)
 
+/datum/computer/file/embedded_program/airlock/docking/proc/enable_mech_regulators()
+	enable_mech_regulation()
+
+/datum/computer/file/embedded_program/airlock/docking/proc/disable_mech_regulators()
+	disable_mech_regulation()
+
 /datum/computer/file/embedded_program/airlock/docking/proc/open_doors()
 	toggleDoor(memory["interior_status"], tag_interior_door, memory["secure"], "open")
 	toggleDoor(memory["exterior_status"], tag_exterior_door, memory["secure"], "open")

code/game/machinery/embedded_controller/airlock_program.dm

@@ -16,6 +16,7 @@
 	var/tag_chamber_sensor
 	var/tag_exterior_sensor
 	var/tag_interior_sensor
+	var/tag_mech_sensor
 
 	var/state = STATE_WAIT
 	var/target_state = TARGET_NONE
@@ -41,6 +42,7 @@
 		tag_chamber_sensor = controller.tag_chamber_sensor? controller.tag_chamber_sensor : "[id_tag]_sensor"
 		tag_exterior_sensor = controller.tag_exterior_sensor
 		tag_interior_sensor = controller.tag_interior_sensor
+		tag_mech_sensor = controller.tag_mech_sensor? controller.tag_mech_sensor : "[id_tag]_mech"
 		memory["secure"] = controller.tag_secure
 
 		spawn(10)
@@ -293,6 +295,11 @@
 			signalDoor(tag_exterior_door, command)
 			signalDoor(tag_interior_door, command)
 
+/datum/computer/file/embedded_program/airlock/proc/enable_mech_regulation()
+	signalDoor(tag_mech_sensor, "enable")
+
+/datum/computer/file/embedded_program/airlock/proc/disable_mech_regulation()
+	signalDoor(tag_mech_sensor, "disable")
 
 /*----------------------------------------------------------
 toggleDoor()

code/game/machinery/embedded_controller/docking_program_multi.dm

@@ -168,9 +168,11 @@
 			if (!override_enabled)
 				stop_cycling()
 				close_doors()
+				disable_mech_regulation()
 
 		if ("finish_docking")
 			if (!override_enabled)
+				enable_mech_regulation()
 				open_doors()
 
 		if ("finish_undocking")

code/game/mecha/mech_sensor.dm

@@ -0,0 +1,86 @@
+/obj/machinery/mech_sensor
+	icon = 'icons/obj/airlock_machines.dmi'
+	icon_state = "airlock_sensor_off"
+	name = "mechatronic sensor"
+	desc = "Regulates mech movement."
+	anchored = 1
+	density = 1
+	throwpass = 1
+	use_power = 1
+	layer = 3.3
+	power_channel = EQUIP
+	var/on = 0
+	var/id_tag = null
+
+	var/frequency = 1379
+	var/datum/radio_frequency/radio_connection
+
+/obj/machinery/mech_sensor/CanPass(atom/movable/mover, turf/target, height=0, air_group=0)
+	if(!src.enabled()) return 1
+	if(air_group || (height==0)) return 1
+
+	if ((get_dir(loc, target) & dir) && src.is_blocked(mover))
+		src.give_feedback(mover)
+		return 0
+	return 1
+
+/obj/machinery/mech_sensor/proc/is_blocked(O as obj)
+	return istype(O, /obj/mecha) || istype(O, /obj/vehicle)
+
+/obj/machinery/mech_sensor/proc/give_feedback(O as obj)
+	var/block_message = "<span class='warning'>Movement control overridden. Area denial active.</span>"
+	var/feedback_timer = 0
+	if(feedback_timer)
+		return
+
+	if(istype(O, /obj/mecha))
+		var/obj/mecha/R = O
+		if(R && R.occupant)
+			R.occupant << block_message
+	else if(istype(O, /obj/vehicle/train/cargo/engine))
+		var/obj/vehicle/train/cargo/engine/E = O
+		if(E && E.load && E.is_train_head())
+			E.load << block_message
+
+	feedback_timer = 1
+	spawn(5) //Without this timer the feedback becomes horribly spamy
+		feedback_timer = 0
+
+/obj/machinery/mech_sensor/proc/enabled()
+	return on && !(stat & NOPOWER)
+
+/obj/machinery/mech_sensor/power_change()
+	var/old_stat = stat
+	..()
+	if(old_stat != stat)
+		update_icon()
+
+/obj/machinery/mech_sensor/update_icon(var/safety = 0)
+	if (enabled())
+		icon_state = "airlock_sensor_on"
+	else
+		icon_state = "airlock_sensor_off"
+
+/obj/machinery/mech_sensor/initialize()
+	set_frequency(frequency)
+
+/obj/machinery/mech_sensor/proc/set_frequency(new_frequency)
+	if(radio_connection)
+		radio_controller.remove_object(src, frequency)
+	frequency = new_frequency
+	if(frequency)
+		radio_connection = radio_controller.add_object(src, frequency)
+
+/obj/machinery/mech_sensor/receive_signal(datum/signal/signal)
+	if(stat & NOPOWER)
+		return
+
+	if(!signal.data["tag"] || (signal.data["tag"] != id_tag))
+		return
+
+	if(signal.data["command"] == "enable")
+		on = 1
+	else if (signal.data["command"] == "disable")
+		on = 0
+
+	update_icon()