Clearer message for devices blocks (#669)

docs/reference/devices.md

@@ -2,6 +2,12 @@
 
 Control a phone with the @boardname@ via Bluetooth.
 
+## ~ hint
+
+**App required** You must use one of the [micro:bit apps](https://microbit.org/guide/mobile/) to use this functionality.
+
+## ~
+
 ```cards
 devices.tellCameraTo(MesCameraEvent.TakePhoto);
 devices.tellRemoteControlTo(MesRemoteControlEvent.play);

docs/reference/devices/on-gamepad-button.md

@@ -3,9 +3,8 @@
 Register code to run when the @boardname@ receives a command from the paired gamepad.
 
 ## ~hint
-![](/static/bluetooth/Bluetooth_SIG.png)
 
-For another device like a smartphone to use any of the Bluetooth "services" which the @boardname@ has, it must first be [paired with the @boardname@](/reference/bluetooth/bluetooth-pairing). Once paired, the other device may connect to the @boardname@ and exchange data relating to many of the @boardname@'s features.
+**App required** You must use one of the [micro:bit apps](https://microbit.org/guide/mobile/) to use this functionality.
 
 ## ~
 

docs/reference/devices/on-notified.md

@@ -3,9 +3,8 @@
 Register code to run when the signal strength of the paired device changes.
 
 ## ~hint
-![](/static/bluetooth/Bluetooth_SIG.png)
 
-For another device like a smartphone to use any of the Bluetooth "services" which the @boardname@ has, it must first be [paired with the @boardname@](/reference/bluetooth/bluetooth-pairing). Once paired, the other device may connect to the @boardname@ and exchange data relating to many of the @boardname@'s features.
+**App required** You must use one of the [micro:bit apps](https://microbit.org/guide/mobile/) to use this functionality.
 
 ## ~
 

docs/reference/devices/on-signal-strength-changed.md

@@ -3,9 +3,8 @@
 Register code to run when the signal strength of the paired device changes.
 
 ## ~hint
-![](/static/bluetooth/Bluetooth_SIG.png)
 
-For another device like a smartphone to use any of the Bluetooth "services" which the @boardname@ has, it must first be [paired with the @boardname@](/reference/bluetooth/bluetooth-pairing). Once paired, the other device may connect to the @boardname@ and exchange data relating to many of the @boardname@'s features.
+**App required** You must use one of the [micro:bit apps](https://microbit.org/guide/mobile/) to use this functionality.
 
 ## ~
 

docs/reference/devices/raise-alert-to.md

@@ -3,9 +3,8 @@
 Raise an alert on a remote device.
 
 ## ~hint
-![](/static/bluetooth/Bluetooth_SIG.png)
 
-For another device like a smartphone to use any of the Bluetooth "services" which the @boardname@ has, it must first be [paired with the @boardname@](/reference/bluetooth/bluetooth-pairing). Once paired, the other device may connect to the @boardname@ and exchange data relating to many of the @boardname@'s features.
+**App required** You must use one of the [micro:bit apps](https://microbit.org/guide/mobile/) to use this functionality.
 
 ## ~
 

docs/reference/devices/signal-strength.md

@@ -3,9 +3,8 @@
 Returns the signal strength reported by the paired device from ``0`` (no signal) to ``4`` (full strength).
 
 ## ~hint
-![](/static/bluetooth/Bluetooth_SIG.png)
 
-For another device like a smartphone to use any of the Bluetooth "services" which the @boardname@ has, it must first be [paired with the @boardname@](/reference/bluetooth/bluetooth-pairing). Once paired, the other device may connect to the @boardname@ and exchange data relating to many of the @boardname@'s features.
+**App required** You must use one of the [micro:bit apps](https://microbit.org/guide/mobile/) to use this functionality.
 
 ## ~
 

docs/reference/devices/tell-camera-to.md

@@ -3,9 +3,8 @@
 Access the photo/video-taking functionality of a remote device using the ``tell camera to`` function.
 
 ## ~hint
-![](/static/bluetooth/Bluetooth_SIG.png)
 
-For another device like a smartphone to use any of the Bluetooth "services" which the @boardname@ has, it must first be [paired with the @boardname@](/reference/bluetooth/bluetooth-pairing). Once paired, the other device may connect to the @boardname@ and exchange data relating to many of the @boardname@'s features.
+**App required** You must use one of the [micro:bit apps](https://microbit.org/guide/mobile/) to use this functionality.
 
 ## ~
 

docs/reference/devices/tell-remote-control-to.md

@@ -3,9 +3,8 @@
 Control the presentation of media content available on a remote device using the `tell remote control` to function.
 
 ## ~hint
-![](/static/bluetooth/Bluetooth_SIG.png)
 
-For another device like a smartphone to use any of the Bluetooth "services" which the @boardname@ has, it must first be [paired with the @boardname@](/reference/bluetooth/bluetooth-pairing). Once paired, the other device may connect to the @boardname@ and exchange data relating to many of the @boardname@'s features.
+**App required** You must use one of the [micro:bit apps](https://microbit.org/guide/mobile/) to use this functionality.
 
 ## ~
 

libs/devices/pxt.json

@@ -1,6 +1,6 @@
 {
     "name": "devices",
-    "description": "Camera, remote control and other Bluetooth services",
+    "description": "Camera, remote control and other Bluetooth services. App required.",
     "files": [
         "README.md",
         "enums.d.ts",