diff --git a/www/js/main.js b/www/js/main.js
index dadeca3..dee42b2 100644
--- a/www/js/main.js
+++ b/www/js/main.js
@@ -4,7 +4,8 @@
 
 var $$ = Dom7;
 
-// Run platform-specific setup code for Cordova or NW.js
+// Detect platform and run platform-specific setup code
+// for Cordova, NW.js, or the browser
 initPlatform();
 
 var app = new Framework7({
@@ -44,10 +45,88 @@ router.on("pageInit", function (pagedata) {
     }
 });
 
+/**
+ * Check if there is a valid API key stored locally.
+ * @param {function} callback A function that will be called with a boolean argument indicating if the key is valid.
+ * @return {undefined}
+ */
+function checkKey(callback) {
+    if (localStorage.getItem("key") === null) {
+        callback(false);
+        return;
+    }
+
+    callAPI("checkkey", {
+        key: localStorage.getItem("key")
+    }, function (data) {
+        var currentTimestamp = Math.floor(Date.now() / 1000);
+        // Check if the key is valid and has at least one day before expiry
+        // If someone leaves the app open longer than 24 hours and the key is
+        // not renewed, there might be bugs.
+        if (data.valid == true && data.expires > (currentTimestamp + (60 * 60 * 24))) {
+            callback(true);
+            return;
+        }
+        callback(false);
+    }, function (msg) {
+        callback(false);
+    });
+}
+
+/**
+ * Attempt to get a new API key using stored credentials.
+ * @param {function} callback A function that will be called with a boolean argument indicating if the attempt was successful.
+ * @return {undefined}
+ */
+function refreshKey(callback) {
+    if (localStorage.getItem("username") === null || localStorage.getItem("password") === null) {
+        callback(false);
+        return;
+    }
+
+    callAPI("getkey", {
+        username: localStorage.getItem("username"),
+        password: localStorage.getItem("password"),
+    }, function (data) {
+        localStorage.setItem("key", data.key);
+        callback(true);
+    }, function (msg) {
+        callback(false);
+    });
+}
+
 
 if (localStorage.getItem("configured") == null) {
     // Open the setup page
     router.navigate("/setup/0");
 } else {
-    router.navigate("/home");
+    checkKey(function (valid) {
+        if (valid) {
+            router.navigate("/home");
+
+            // Check and refresh API key as needed
+            // Should mitigate key expiration if the app is left open for
+            // a long time when the key is almost expired
+            setInterval(function () {
+                checkKey(function (valid) {
+                    if (!valid) {
+                        refreshKey(function (ok) {
+                            if (!ok) {
+                                router.navigate("/setup/0");
+                            }
+                        });
+                    }
+                });
+            }, 1000 * 60 * 5);
+        } else {
+            refreshKey(function (ok) {
+                if (ok) {
+                    router.navigate("/home");
+                } else {
+                    //router.navigate("/setup/0");
+                }
+            });
+        }
+    });
+
 }
\ No newline at end of file