added 2 more activities

docs/maker/intruder-detector.md

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+# Intruder Detector
+
+This program will activate an alarm when an object moves in front of the Ultrasonic Sensor.
+
+TODO support for event when value changes
+
+```blocks
+input.ultrasonic4.onObjectNear(function () {
+    music.playSoundUntilDone(music.sounds(Sounds.PowerUp))
+})
+```

docs/maker/security-gadget.md

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+# Security Gadget
+
+This program will activate an alarm when an object is lifted from the Touch Sensor.
+
+```blocks
+input.touchSensor1.onEvent(TouchSensorEvent.Released, function () {
+    music.playSoundUntilDone(music.sounds(Sounds.PowerUp))
+})
+```