diff --git a/avr/apps/co2_watch/0BUILD b/avr/apps/co2_watch/0BUILD
new file mode 100644
index 0000000..593fe80
--- /dev/null
+++ b/avr/apps/co2_watch/0BUILD
@@ -0,0 +1,15 @@
+<?xml?>
+
+<gwbuild>
+
+  <subdirs>
+  </subdirs>
+
+  <extradist>
+    main.asm
+  </extradist>
+  
+
+</gwbuild>
+
+
diff --git a/avr/apps/co2_watch/main.asm b/avr/apps/co2_watch/main.asm
new file mode 100644
index 0000000..f5d5120
--- /dev/null
+++ b/avr/apps/co2_watch/main.asm
@@ -0,0 +1,150 @@
+; ***************************************************************************
+; copyright   : (C) 2026 by Martin Preuss
+; email       : martin@libchipcard.de
+;
+; ***************************************************************************
+; * This file is part of the project "AqHome".                              *
+; * Please see toplevel file COPYING of that project for license details.   *
+; ***************************************************************************
+
+
+
+; ***************************************************************************
+; defines
+
+.equ APPCO2WATCH_WARN = 1000
+.equ APPCO2WATCH_CRIT = 2000
+
+.equ APPCO2WATCH_LEVEL_OK   = 0
+.equ APPCO2WATCH_LEVEL_WARN = 1
+.equ APPCO2WATCH_LEVEL_CRIT = 2
+
+.equ APPCO2WATCH_LED_ONTIME  = 3
+.equ APPCO2WATCH_LED_OFFTIME = 7
+
+
+
+; ***************************************************************************
+; data
+
+.dseg
+
+appCo2WatchDatBegin:
+  appCo2WatchLimitWarnLo: .byte 1
+  appCo2WatchLimitWarnHi: .byte 1
+  appCo2WatchLimitCritLo: .byte 1
+  appCo2WatchLimitCritHi: .byte 1
+appCo2WatchDatEnd:
+
+
+
+
+; ***************************************************************************
+; code
+
+.cseg
+
+
+AppCo2Watch_Init:
+  ldi r16, LOW(APPCO2WATCH_WARN)
+  ldi r17, HIGH(APPCO2WATCH_WARN)
+  sts appCo2WatchLimitWarnLo, r16
+  sts appCo2WatchLimitWarnHi, r17
+
+  ldi r16, LOW(APPCO2WATCH_CRIT)
+  ldi r17, HIGH(APPCO2WATCH_CRIT)
+  sts appCo2WatchLimitCritLo, r16
+  sts appCo2WatchLimitCritHi, r17
+
+  ldi r18, 50  ; 5secs on
+  ldi r19, 1   ; 100ms off
+  ldi r20, 1   ; go into standard heartbeat mode after period
+  bigcall LED1_SetTiming
+
+  ldi r18, 40  ; 4secs on
+  ldi r19, 1   ; 100ms off
+  ldi r20, 255 ; turn off after period
+  bigcall LED2_SetTiming
+
+  ldi r18, 30  ; 3secs on
+  ldi r19, 1   ; 100ms off
+  ldi r20, 255 ; turn off after period
+  bigcall LED3_SetTiming
+  
+  sec
+  ret
+; @end
+
+
+
+AppCo2Watch_OnEveryMinute:
+  ldi r16, SGP30_VALUE_CO2
+  bigcall SGP30_GetValue   ; R19:R18=value, R21:R20=denom
+  ldi r23, APPCO2WATCH_LEVEL_OK
+  brcc AppCo2Watch_OnEveryMinute_ret
+  lds r16, appCo2WatchLimitCritLo
+  lds r17, appCo2WatchLimitCritHi
+  cp r18, r16
+  cpc r19, r17
+  brcs AppCo2Watch_OnEveryMinute_next ; below critical
+  ldi r23, APPCO2WATCH_LEVEL_CRIT
+  rjmp AppCo2Watch_OnEveryMinute_setLed
+AppCo2Watch_OnEveryMinute_next:
+  lds r16, appCo2WatchLimitWarnLo
+  lds r17, appCo2WatchLimitWarnHi
+  cp r18, r16
+  cpc r19, r17
+  brcs AppCo2Watch_OnEveryMinute_setLed
+  ldi r23, APPCO2WATCH_LEVEL_WARN
+AppCo2Watch_OnEveryMinute_setLed:
+  cpi r23, APPCO2WATCH_LEVEL_OK
+  breq AppCo2Watch_OnEveryMinute_setGreen
+  cpi r23, APPCO2WATCH_LEVEL_WARN
+  breq AppCo2Watch_OnEveryMinute_setYellow
+  cpi r23, APPCO2WATCH_LEVEL_CRIT
+  breq AppCo2Watch_OnEveryMinute_setRed
+AppCo2Watch_OnEveryMinute_setGreen:
+  rcall appCo2WatchLed2Off
+  rcall appCo2WatchLed3Off
+  rjmp AppCo2Watch_OnEveryMinute_ret
+AppCo2Watch_OnEveryMinute_setYellow:
+  rcall appCo2WatchLed2On
+  rcall appCo2WatchLed3Off
+  rjmp AppCo2Watch_OnEveryMinute_ret
+AppCo2Watch_OnEveryMinute_setRed:
+  rcall appCo2WatchLed2Off
+  rcall appCo2WatchLed3On
+AppCo2Watch_OnEveryMinute_ret:
+  ret
+; @end
+
+
+
+
+appCo2WatchLed2On:
+  ldi r18, APPCO2WATCH_LED_ONTIME
+  ldi r19, APPCO2WATCH_LED_OFFTIME
+  clr r20
+  bigjmp Led2_SetTiming
+
+appCo2WatchLed2Off:
+  clr r18
+  clr r19
+  clr r20
+  bigjmp Led2_SetTiming
+
+appCo2WatchLed3On:
+  ldi r18, APPCO2WATCH_LED_ONTIME
+  ldi r19, APPCO2WATCH_LED_OFFTIME
+  clr r20
+  bigjmp Led3_SetTiming
+
+appCo2WatchLed3Off:
+  clr r18
+  clr r19
+  clr r20
+  bigjmp Led3_SetTiming
+
+
+
+
diff --git a/avr/devices/all/apps_1m.asm b/avr/devices/all/apps_1m.asm
index 36e9af0..99f5507 100644
--- a/avr/devices/all/apps_1m.asm
+++ b/avr/devices/all/apps_1m.asm
@@ -25,6 +25,10 @@ appsOnEveryMinute:
   bigcall AppStats_OnEveryMinute
 #endif
 
+#ifdef APPS_CO2WATCH
+  bigcall AppCo2Watch_OnEveryMinute
+#endif
+
   ret
 ; @end
 
diff --git a/avr/devices/all/apps_include.asm b/avr/devices/all/apps_include.asm
index 60b7bac..83253ac 100644
--- a/avr/devices/all/apps_include.asm
+++ b/avr/devices/all/apps_include.asm
@@ -18,6 +18,11 @@
 .include "apps/motion/main.asm"
 #endif
 
+#ifdef APPS_CO2WATCH
+.include "apps/co2_watch/main.asm"
+#endif
+
+
 #ifdef APPS_DOOR
 #ifndef APPS_MOTION
 .include "modules/f_keepup/main.asm"
diff --git a/avr/devices/all/apps_init.asm b/avr/devices/all/apps_init.asm
index 7489175..5cc8fd4 100644
--- a/avr/devices/all/apps_init.asm
+++ b/avr/devices/all/apps_init.asm
@@ -63,6 +63,10 @@ appsInit:
   bigcall AppMotionLight_Init
 #endif
 
+#ifdef APPS_CO2WATCH
+  bigcall AppCo2Watch_Init
+#endif
+
   ; done
   ret
 ; @end