Refactor alert script

scripts/alert

@@ -1,8 +1,27 @@
 #!/usr/bin/env bash
 
+# Devices to check -- if populated and up, no notifications are sent.
+readonly DEVICES=()
 readonly RECIPIENT="${NOTIFICATION_RECIPIENT}"
 
+check_devices() {
+  for device in "${DEVICES[@]}"; do
+    if ping -c 1 -w 1 "${device}" &> "/dev/null"; then
+      return 0
+    fi
+  done
+
+  return 255
+}
+
 main() {
+  # If devices are present, don't notify.
+  if (( "${#DEVICES[@]}" )); then
+    if check_devices; then
+      exit 0
+    fi
+  fi
+
   echo "${HOSTNAME}: motion detected at $(date '+%Y-%m-%dT%H:%M:%S%:z')." | \
     mutt -s "${HOSTNAME}: Motion Detected" \
 	 -- "${RECIPIENT}"