diff --git a/js/ble/gatt.js b/js/ble/gatt.js
new file mode 100644
index 0000000..b180c67
--- /dev/null
+++ b/js/ble/gatt.js
@@ -0,0 +1,48 @@
+const GATT = Object.freeze({
+  Battery: Object.freeze({
+    service: 0x180f,
+    level: "0x2A19", // Battery Level (Read / Notify)
+  }),
+
+  HeartRate: Object.freeze({
+    service: 0x180d,
+    measurement: "0x2A37", // Heart Rate Measurement (Notify)
+    bodySensorLocation: "0x2A38", // Body Sensor Location (Read)
+    controlPoint: "0x2A39", // Heart Rate Control Point (Write)
+  }),
+
+  Cadence: Object.freeze({
+    service: "0x1816",
+    measurement: "0x2A5B", // CSC Measurement (Notify)
+    feature: "0x2A5C", // CSC Feature (Read)
+    location: "0x2A5D", // Sensor Location (Read)
+  }),
+
+  PowerMeter: Object.freeze({
+    service: "0x1818",
+    measurement: "0x2A63", // Cycling Power Measurement (Notify)
+    feature: "0x2A64", // Cycling Power Feature (Read)
+    controlPoint: "0x2A65", // Cycling Power Control Point (Write)
+    location: "0x2A66", // Sensor Location (Read)
+  }),
+
+  SmartTrainer: Object.freeze({
+    service: "0x1826", // Fitness Machine Service
+    status: "0x2AD9", // Fitness Machine Status (Notify)
+    controlPoint: "0x2ACC", // Fitness Machine Control Point (Write/Indicate)
+    feature: "0x2ADA", // Fitness Machine Feature (Read)
+    indoorBikeData: "0x2ADB", // Indoor Bike Data (Notify)
+    trainingStatus: "0x2ADC", // Training Status (Notify)
+    supportedResistance: "0x2ADD", // Supported Resistance Level (Read)
+  }),
+
+  DeviceInfo: Object.freeze({
+    service: 0x180a, // Device Information Service
+    manufacturerName: "0x2A29", // Manufacturer Name String (Read)
+    modelNumber: "0x2A24", // Model Number String (Read)
+    serialNumber: "0x2A25", // Serial Number String (Read)
+    firmwareRevision: "0x2A26", // Firmware Revision String (Read)
+  }),
+});
+
+export { GATT };
diff --git a/js/ble/index.js b/js/ble/index.js
new file mode 100644
index 0000000..e1cd735
--- /dev/null
+++ b/js/ble/index.js
@@ -0,0 +1,17 @@
+import { GATT } from "./gatt.js";
+
+const hrSensorOptions = {
+  filters: [{ services: [GATT.HeartRate.service] }],
+  optionalServices: [GATT.DeviceInfo.service, GATT.Battery.service],
+};
+
+const requestHRSensor = async () => {
+  try {
+    return await navigator.bluetooth.requestDevice(hrSensorOptions);
+  } catch (err) {
+    console.log(err);
+    return null;
+  }
+};
+
+export { requestHRSensor };
diff --git a/js/main.js b/js/main.js
index 33d4839..e1271e2 100644
--- a/js/main.js
+++ b/js/main.js
@@ -1,18 +1,10 @@
 import { Core } from "./device/index.js";
+import { requestHRSensor } from "./ble/index.js";
 
 const startButton = document.getElementById("start");
 const hrButton = document.getElementById("hr");
 
 hrButton.addEventListener("click", async () => {
-  const hrOptions = {
-    // Show only devices that advertise the Heart Rate service (0x180D)
-    filters: [{ services: [0x180d] }],
-
-    // After the user picks a device we also want to read the Device
-    // Information service (optional, no extra prompt)
-    optionalServices: [0x180a], // Device Information
-  };
-
   function parseHeartRate(dataView) {
     // Flags are in the first byte
     const flags = dataView.getUint8(0);
@@ -25,7 +17,9 @@ hrButton.addEventListener("click", async () => {
   }
 
   try {
-    const device = await navigator.bluetooth.requestDevice(hrOptions);
+    const device = await requestHRSensor();
+    console.log("D", device);
+    if (!device) return;
     const server = await device.gatt.connect();
 
     const partialCore = new Core({
diff --git a/js/ui/index.js b/js/ui/index.js
new file mode 100644
index 0000000..fbe6989
--- /dev/null
+++ b/js/ui/index.js
@@ -0,0 +1,5 @@
+const connectHRSensor = () => {};
+const connectCadenceSensor = () => {};
+const connectTrainer = () => {};
+
+export { connectHRSensor, connectCadenceSensor, connectTrainer };