diff --git a/src/actor.asm b/src/actor.asm
index 3fcc49b..7ee2752 100644
--- a/src/actor.asm
+++ b/src/actor.asm
@@ -26,6 +26,7 @@
 .INCLUDE "macros.inc"
 .INCLUDE "ppu.inc"
 
+.IMPORT FuncA_Actor_TickAllDevices
 .IMPORT FuncA_Actor_TickBadBat
 .IMPORT FuncA_Actor_TickBadBeetleHorz
 .IMPORT FuncA_Actor_TickBadBeetleVert
@@ -701,20 +702,20 @@ _NoHit:
     D_END
 .ENDPROC
 
-;;; Performs per-frame updates for each actor in the room.
-.EXPORT FuncA_Actor_TickAllActors
-.PROC FuncA_Actor_TickAllActors
+;;; Performs per-frame updates for each device and actor in the room.
+.EXPORT FuncA_Actor_TickAllDevicesAndActors
+.PROC FuncA_Actor_TickAllDevicesAndActors
     ldx #kMaxActors - 1
     @loop:
     jsr FuncA_Actor_TickOneActor  ; preserves X
     dex
     bpl @loop
-    rts
+    jmp FuncA_Actor_TickAllDevices
 .ENDPROC
 
-;;; Performs per-frame updates for each smoke actor in the room.
-.EXPORT FuncA_Actor_TickAllSmokeActors
-.PROC FuncA_Actor_TickAllSmokeActors
+;;; Performs per-frame updates for each device and smoke actor in the room.
+.EXPORT FuncA_Actor_TickAllDevicesAndSmokeActors
+.PROC FuncA_Actor_TickAllDevicesAndSmokeActors
     ldx #kMaxActors - 1
     @loop:
     lda Ram_ActorType_eActor_arr, x
@@ -724,7 +725,7 @@ _NoHit:
     @continue:
     dex
     bpl @loop
-    rts
+    jmp FuncA_Actor_TickAllDevices
 .ENDPROC
 
 ;;; Performs per-frame updates for one actor.
diff --git a/src/boss.asm b/src/boss.asm
index e3d0225..39f3376 100644
--- a/src/boss.asm
+++ b/src/boss.asm
@@ -29,9 +29,11 @@
 .INCLUDE "room.inc"
 .INCLUDE "sample.inc"
 
+.IMPORT FuncA_Room_LockDoorDevice
 .IMPORT FuncA_Room_MachineResetHalt
 .IMPORT FuncA_Room_PlaySfxBreakerRising
 .IMPORT FuncA_Room_SpawnUpgradeDevice
+.IMPORT FuncA_Room_UnlockDoorDevice
 .IMPORT Func_DivMod
 .IMPORT Func_FindEmptyActorSlot
 .IMPORT Func_GetRandomByte
@@ -39,7 +41,6 @@
 .IMPORT Func_InitActorSmokeExplosion
 .IMPORT Func_InitActorSmokeParticle
 .IMPORT Func_IsFlagSet
-.IMPORT Func_LockDoorDevice
 .IMPORT Func_MarkRoomSafe
 .IMPORT Func_Noop
 .IMPORT Func_PlaySfxExplodeBig
@@ -49,7 +50,6 @@
 .IMPORT Func_SetFlag
 .IMPORT Func_SetMachineIndex
 .IMPORT Func_ShakeRoom
-.IMPORT Func_UnlockDoorDevice
 .IMPORT Ram_ActorType_eActor_arr
 .IMPORT Ram_DeviceAnim_u8_arr
 .IMPORT Ram_DeviceTarget_byte_arr
@@ -114,7 +114,7 @@ Zp_BossPhaseTimer_u8: .res 1
     sta Zp_BossPhaseTimer_u8
     ;; Lock the door for now.
     ldx #kBossDoorDeviceIndex  ; param: device index
-    jsr Func_LockDoorDevice
+    jsr FuncA_Room_LockDoorDevice
     ;; Check if the boss has been defeated yet.
     ldy #sBoss::Boss_eFlag
     lda (Zp_Current_sBoss_ptr), y
@@ -160,7 +160,7 @@ _BreakerAlreadyDone:
     sta Ram_DeviceType_eDevice_arr + kBossBreakerDeviceIndex
     ;; Unlock the door.
     ldx #kBossDoorDeviceIndex  ; param: device index
-    jsr Func_UnlockDoorDevice
+    jsr FuncA_Room_UnlockDoorDevice
     ;; Set and return the initial phase.
     lda #eBossPhase::Done
     sta Zp_Boss_eBossPhase
@@ -364,7 +364,7 @@ _FlipBreaker:
     bne @done
     ;; Unlock the door.
     ldx #kBossDoorDeviceIndex  ; param: device index
-    jsr Func_UnlockDoorDevice
+    jsr FuncA_Room_UnlockDoorDevice
     ;; Proceed to the next phase.
     lda #eBossPhase::Done
     sta Zp_Boss_eBossPhase
diff --git a/src/console.asm b/src/console.asm
index 6d5a7a3..35e6f41 100644
--- a/src/console.asm
+++ b/src/console.asm
@@ -36,7 +36,7 @@
 .INCLUDE "window.inc"
 
 .IMPORT DataA_Console_DiagramBank_u8_arr
-.IMPORT FuncA_Actor_TickAllSmokeActors
+.IMPORT FuncA_Actor_TickAllDevicesAndSmokeActors
 .IMPORT FuncA_Console_DrawFieldCursor
 .IMPORT FuncA_Console_MoveFieldCursor
 .IMPORT FuncA_Console_WriteDiagramTransferDataForCurrentMachine
@@ -59,7 +59,6 @@
 .IMPORT Func_SetLastSpawnPoint
 .IMPORT Func_SetMachineIndex
 .IMPORT Func_SetMusicVolumeForCurrentRoom
-.IMPORT Func_TickAllDevices
 .IMPORT Func_Window_GetRowPpuAddr
 .IMPORT Func_Window_PrepareRowTransfer
 .IMPORT Func_Window_ScrollDown
@@ -272,8 +271,7 @@ _Tick:
 ;;; Calls per-frame tick functions that should still happen even when the
 ;;; machine console is open.
 .PROC FuncM_ConsoleTick
-    jsr_prga FuncA_Actor_TickAllSmokeActors
-    jsr Func_TickAllDevices
+    jsr_prga FuncA_Actor_TickAllDevicesAndSmokeActors
     jsr_prga FuncA_Machine_ConsoleTickOrExecuteAll
     jmp_prga FuncA_Room_CallRoomTick
 .ENDPROC
diff --git a/src/cutscene.asm b/src/cutscene.asm
index 28e6cdb..6ef37b9 100644
--- a/src/cutscene.asm
+++ b/src/cutscene.asm
@@ -61,15 +61,14 @@
 .IMPORT DataA_Cutscene_TownHouse4BreakerLava_sCutscene
 .IMPORT DataA_Cutscene_TownOutdoorsGetCaught_sCutscene
 .IMPORT DataA_Cutscene_TownOutdoorsOrcAttack_sCutscene
-.IMPORT FuncA_Actor_TickAllActors
-.IMPORT FuncA_Actor_TickAllSmokeActors
+.IMPORT FuncA_Actor_TickAllDevicesAndActors
+.IMPORT FuncA_Actor_TickAllDevicesAndSmokeActors
 .IMPORT FuncA_Avatar_RagdollMove
 .IMPORT FuncA_Room_CallRoomTick
 .IMPORT FuncM_DrawObjectsForRoomAndProcessFrame
 .IMPORT FuncM_ScrollTowardsGoal
 .IMPORT Func_PlaySfxSample
 .IMPORT Func_ShakeRoom
-.IMPORT Func_TickAllDevices
 .IMPORT Main_Dialog_WithinCutscene
 .IMPORT Main_Explore_Continue
 .IMPORT Ram_ActorFlags_bObj_arr
@@ -155,8 +154,7 @@ _GameLoop:
     jsr_prga FuncA_Cutscene_ExecuteAllForks  ; returns C, T1T0, and Y
     bcs _Finish
     jsr FuncM_ScrollTowardsGoal
-    jsr_prga FuncA_Actor_TickCutsceneActors
-    jsr Func_TickAllDevices
+    jsr_prga FuncA_Actor_TickAllDevicesAndCutsceneActors
 _MaybeTickRoom:
     bit Zp_CutsceneFlags_bCutscene
     .assert bCutscene::RoomTick = bProc::Negative, error
@@ -178,13 +176,13 @@ _Finish:
 
 .SEGMENT "PRGA_Actor"
 
-;;; Ticks all actors if bCutscene::TickAllActors is set; otherwise, ticks smoke
-;;; actors only.
-.PROC FuncA_Actor_TickCutsceneActors
+;;; Ticks all devices and actors if bCutscene::TickAllActors is set; otherwise,
+;;; ticks devices and smoke actors only.
+.PROC FuncA_Actor_TickAllDevicesAndCutsceneActors
     lda Zp_CutsceneFlags_bCutscene
     and #bCutscene::TickAllActors
-    jeq FuncA_Actor_TickAllSmokeActors
-    jmp FuncA_Actor_TickAllActors
+    jeq FuncA_Actor_TickAllDevicesAndSmokeActors
+    jmp FuncA_Actor_TickAllDevicesAndActors
 .ENDPROC
 
 ;;;=========================================================================;;;
diff --git a/src/device.asm b/src/device.asm
index cbaec01..f318a48 100644
--- a/src/device.asm
+++ b/src/device.asm
@@ -74,12 +74,12 @@ Ram_DeviceAnim_u8_arr: .res kMaxDevices
 
 ;;;=========================================================================;;;
 
-.SEGMENT "PRG8"
+.SEGMENT "PRGA_Actor"
 
 ;;; Decrements the animation counter for each device in the room (if that
 ;;; counter is nonzero; otherwise, leaves it at zero).
-.EXPORT Func_TickAllDevices
-.PROC Func_TickAllDevices
+.EXPORT FuncA_Actor_TickAllDevices
+.PROC FuncA_Actor_TickAllDevices
     ldx #kMaxDevices - 1
 _Loop:
     ;; If the animation counter is nonzero, decrement it.
@@ -100,6 +100,10 @@ _Continue:
     rts
 .ENDPROC
 
+;;;=========================================================================;;;
+
+.SEGMENT "PRG8"
+
 ;;; Returns the index of the device whose block the point stored in
 ;;; Zp_PointX_i16 and Zp_PointY_i16 is in, if any.
 ;;; @return N Set if there was no device nearby, cleared otherwise.
diff --git a/src/devices/boiler.asm b/src/devices/boiler.asm
index 5badae5..bc8538e 100644
--- a/src/devices/boiler.asm
+++ b/src/devices/boiler.asm
@@ -60,15 +60,13 @@
 .EXPORT Func_EmitSteamRightFromPipe
 .PROC Func_EmitSteamRightFromPipe
     jsr Func_FindEmptyActorSlot  ; preserves Y and T0+, returns C and X
-    bcs @done
+    bcs Func_DoNotEmitSteam  ; preserves T0+
     jsr Func_SetPointToPlatformCenter  ; preserves X and T0+
     lda #kTileWidthPx * 3 / 2  ; param: offset
     jsr Func_MovePointRightByA  ; preserves X and T0+
     jsr Func_SetActorCenterToPoint  ; preserves X and T0+
     lda #0  ; param: facing dir
     jmp Func_InitActorProjSteamHorz  ; preserves T0+
-    @done:
-    rts
 .ENDPROC
 
 ;;; Given an 8x8 pixel platform covering the end tile of an upward-facing pipe,
@@ -78,13 +76,18 @@
 .EXPORT Func_EmitSteamUpFromPipe
 .PROC Func_EmitSteamUpFromPipe
     jsr Func_FindEmptyActorSlot  ; preserves Y and T0+, returns C and X
-    bcs @done
+    bcs Func_DoNotEmitSteam  ; preserves T0+
     jsr Func_SetPointToPlatformCenter  ; preserves X and T0+
     lda #kTileHeightPx * 3 / 2  ; param: offset
     jsr Func_MovePointUpByA  ; preserves X and T0+
     jsr Func_SetActorCenterToPoint  ; preserves X and T0+
     jmp Func_InitActorProjSteamUp  ; preserves T0+
-    @done:
+.ENDPROC
+
+;;; No-op function for when a Func_EmitSteam* function above is unable to
+;;; allocate an actor slot for the steam.
+;;; @preserve T0+
+.PROC Func_DoNotEmitSteam
     rts
 .ENDPROC
 
diff --git a/src/devices/door.asm b/src/devices/door.asm
index a8d6d51..59b8553 100644
--- a/src/devices/door.asm
+++ b/src/devices/door.asm
@@ -50,30 +50,32 @@ kPaletteObjDoorway = 0
 
 ;;;=========================================================================;;;
 
-.SEGMENT "PRG8"
+.SEGMENT "PRGA_Room"
 
 ;;; Locks a door device, if not locked already.
 ;;; @param X The device index for the (locked or unlocked) door.
 ;;; @preserve T0+
-.EXPORT Func_LockDoorDevice
-.PROC Func_LockDoorDevice
-    lda #eDevice::Door1Locked
-    cmp Ram_DeviceType_eDevice_arr, x
-    beq @done
-    sta Ram_DeviceType_eDevice_arr, x
-    lda #kDoorAnimCountdown
-    sub Ram_DeviceAnim_u8_arr, x
-    sta Ram_DeviceAnim_u8_arr, x
-    @done:
-    rts
+.EXPORT FuncA_Room_LockDoorDevice
+.PROC FuncA_Room_LockDoorDevice
+    lda #eDevice::Door1Locked  ; param: new device type
+    .assert eDevice::Door1Unlocked > 0, error
+    bne FuncA_Room_LockOrUnlockDoorDevice  ; unconditional; preserves T0+
 .ENDPROC
 
 ;;; Unlocks a door device, if not unlocked already.
 ;;; @param X The device index for the (locked or unlocked) door.
 ;;; @preserve T0+
-.EXPORT Func_UnlockDoorDevice
-.PROC Func_UnlockDoorDevice
-    lda #eDevice::Door1Unlocked
+.EXPORT FuncA_Room_UnlockDoorDevice
+.PROC FuncA_Room_UnlockDoorDevice
+    lda #eDevice::Door1Unlocked  ; param: new device type
+    fall FuncA_Room_LockOrUnlockDoorDevice  ; preserves T0+
+.ENDPROC
+
+;;; Locks or unlocks a door device, if not already in the desired state.
+;;; @param A The device type to change to (Door1Locked or Door1Unlocked).
+;;; @param X The device index for the door.
+;;; @preserve T0+
+.PROC FuncA_Room_LockOrUnlockDoorDevice
     cmp Ram_DeviceType_eDevice_arr, x
     beq @done
     sta Ram_DeviceType_eDevice_arr, x
diff --git a/src/explore.asm b/src/explore.asm
index 13327b1..a465d77 100644
--- a/src/explore.asm
+++ b/src/explore.asm
@@ -33,7 +33,7 @@
 .INCLUDE "spawn.inc"
 .INCLUDE "tileset.inc"
 
-.IMPORT FuncA_Actor_TickAllActors
+.IMPORT FuncA_Actor_TickAllDevicesAndActors
 .IMPORT FuncA_Avatar_EnterRoomViaDoor
 .IMPORT FuncA_Avatar_EnterRoomViaPassage
 .IMPORT FuncA_Avatar_ExitRoomViaPassage
@@ -64,7 +64,6 @@
 .IMPORT Func_FindDeviceNearPoint
 .IMPORT Func_SetLastSpawnPointToActiveDevice
 .IMPORT Func_SetPointToAvatarCenter
-.IMPORT Func_TickAllDevices
 .IMPORT Func_Window_Disable
 .IMPORT Func_Window_SetUpIrq
 .IMPORT Main_Breaker_UseDevice
@@ -196,8 +195,7 @@ _CheckButtons:
     @continueExploring:
 _Tick:
     jsr FuncM_ScrollTowardsAvatar
-    jsr_prga FuncA_Actor_TickAllActors
-    jsr Func_TickAllDevices
+    jsr_prga FuncA_Actor_TickAllDevicesAndActors
     jsr_prga FuncA_Machine_ExecuteAll
     jsr_prga FuncA_Room_CallRoomTick
     ;; Check if the player avatar is dead:
diff --git a/src/rooms/city_center.asm b/src/rooms/city_center.asm
index 863eb7b..ae6fb5a 100644
--- a/src/rooms/city_center.asm
+++ b/src/rooms/city_center.asm
@@ -63,12 +63,12 @@
 .IMPORT FuncA_Objects_SetShapePosToPlatformTopLeft
 .IMPORT FuncA_Room_MachineResetRun
 .IMPORT FuncA_Room_MachineSemaphoreReset
+.IMPORT FuncA_Room_UnlockDoorDevice
 .IMPORT Func_GetRandomByte
 .IMPORT Func_Noop
 .IMPORT Func_PlaySfxExplodeBig
 .IMPORT Func_SetFlag
 .IMPORT Func_SetMachineIndex
-.IMPORT Func_UnlockDoorDevice
 .IMPORT Main_Breaker_FadeBackToBreakerRoom
 .IMPORT Ppu_ChrObjCity
 .IMPORT Ppu_ChrObjParley
@@ -650,7 +650,7 @@ _SetFlag:
     ldx #eFlag::CityCenterDoorUnlocked  ; param: flag
     jsr Func_SetFlag
     ldx #kLockedDoorDeviceIndex  ; param: device index
-    jsr Func_UnlockDoorDevice
+    jmp FuncA_Room_UnlockDoorDevice
     @done:
     rts
 .ENDPROC
diff --git a/src/rooms/mermaid_hut4.asm b/src/rooms/mermaid_hut4.asm
index c34c569..0d75cf5 100644
--- a/src/rooms/mermaid_hut4.asm
+++ b/src/rooms/mermaid_hut4.asm
@@ -84,12 +84,12 @@
 .IMPORT DataA_Text1_MermaidHut4Florist_Zero2_u8_arr
 .IMPORT DataA_Text1_MermaidHut4Florist_Zero3_u8_arr
 .IMPORT FuncA_Objects_Draw1x1Shape
+.IMPORT FuncA_Room_UnlockDoorDevice
 .IMPORT Func_CountDeliveredFlowers
 .IMPORT Func_DropFlower
 .IMPORT Func_IsFlagSet
 .IMPORT Func_Noop
 .IMPORT Func_SetFlag
-.IMPORT Func_UnlockDoorDevice
 .IMPORT Ppu_ChrObjVillage
 .IMPORT Ram_DeviceType_eDevice_arr
 .IMPORT Sram_CarryingFlower_eFlag
@@ -130,7 +130,7 @@ _Ext_sRoomExt:
     d_addr Passages_sPassage_arr_ptr, 0
     d_addr Enter_func_ptr, FuncC_Mermaid_Hut4_EnterRoom
     d_addr FadeIn_func_ptr, Func_Noop
-    d_addr Tick_func_ptr, Func_Noop
+    d_addr Tick_func_ptr, FuncC_Mermaid_Hut4_TickRoom
     d_addr Draw_func_ptr, FuncC_Mermaid_Hut4_DrawRoom
     D_END
 _TerrainData:
@@ -196,6 +196,16 @@ _Devices_sDevice_arr:
     rts
 .ENDPROC
 
+;;; @prereq PRGA_Room is loaded.
+.PROC FuncC_Mermaid_Hut4_TickRoom
+    flag_bit Sram_ProgressFlags_arr, eFlag::MermaidHut4OpenedCellar
+    beq @done
+    ldx #kCellarDoorDeviceIndex  ; param: device index
+    jsr FuncA_Room_UnlockDoorDevice
+    @done:
+    rts
+.ENDPROC
+
 ;;; Allocates and populates OAM slots for this room.
 ;;; @prereq PRGA_Objects is loaded.
 .PROC FuncC_Mermaid_Hut4_DrawRoom
@@ -383,8 +393,6 @@ _Eleven_sDialog:
 _Twelve_sDialog:
     dlg_Func @func
     @func:
-    ldx #kCellarDoorDeviceIndex  ; param: device index
-    jsr Func_UnlockDoorDevice
     ldx #eFlag::MermaidHut4OpenedCellar  ; param: flag
     jsr Func_SetFlag
     flag_bit Sram_ProgressFlags_arr, eFlag::UpgradeOpBeep