diff --git a/js/device/cadence.js b/js/device/cadence.js
new file mode 100644
index 0000000..7815b5a
--- /dev/null
+++ b/js/device/cadence.js
@@ -0,0 +1,15 @@
+const CadenceQuality = Object.freeze({
+  HIGH: "high",
+  MEDIUM: "medium",
+  LOW: "low",
+  UNKNOWN: "unknown",
+});
+
+function validateCadenceQuality(v) {
+  const set = CadenceQuality;
+  if (!v) return set.UNKNOWN;
+  const vals = Object.values(set);
+  return vals.includes(v) ? v : set.UNKNOWN;
+}
+
+export { validateCadenceQuality, CadenceQuality };
diff --git a/js/device/capabilities/control.js b/js/device/capabilities/control.js
new file mode 100644
index 0000000..20b9425
--- /dev/null
+++ b/js/device/capabilities/control.js
@@ -0,0 +1,34 @@
+import { deepFreeze, isFiniteNumber } from "../../utils";
+import { CyclingPowerCapabilities } from "./cyclingPower.js";
+
+export class Control {
+  constructor({
+    supportsERG = false,
+    controlCharacteristic,
+    maxPowerWatts,
+    minPowerWatts,
+    ergRampRateWattsPerSec,
+    cyclingPower,
+  } = {}) {
+    this.supportsERG = Boolean(supportsERG);
+    this.controlCharacteristic = controlCharacteristic;
+    this.maxPowerWatts = isFiniteNumber(maxPowerWatts)
+      ? Number(maxPowerWatts)
+      : undefined;
+    this.minPowerWatts = isFiniteNumber(minPowerWatts)
+      ? Number(minPowerWatts)
+      : undefined;
+    this.ergRampRateWattsPerSec = isFiniteNumber(ergRampRateWattsPerSec)
+      ? Number(ergRampRateWattsPerSec)
+      : undefined;
+    this.cyclingPower =
+      cyclingPower instanceof CyclingPowerCapabilities
+        ? cyclingPower
+        : cyclingPower
+          ? new CyclingPowerCapabilities(cyclingPower)
+          : undefined;
+    deepFreeze(this);
+  }
+
+  merge = (partial) => new Control(Object.assign({}, this, partial));
+}
diff --git a/js/device/capabilities/core.js b/js/device/capabilities/core.js
new file mode 100644
index 0000000..0a3a010
--- /dev/null
+++ b/js/device/capabilities/core.js
@@ -0,0 +1,35 @@
+import { deepFreeze } from "../../utils";
+
+export class Core {
+  constructor({
+    supportsBattery = false,
+    supportsManufacturerData = false,
+    gattServices,
+    gattCharacteristics,
+    manufacturer,
+    model,
+    firmwareVersion,
+    serial,
+    reconnectOnDisconnect = true,
+    requiresPairing = false,
+  } = {}) {
+    this.supportsBattery = Boolean(supportsBattery);
+    this.supportsManufacturerData = Boolean(supportsManufacturerData);
+    this.gattServices = Array.isArray(gattServices)
+      ? gattServices.slice()
+      : undefined;
+    this.gattCharacteristics =
+      gattCharacteristics && typeof gattCharacteristics === "object"
+        ? Object.assign({}, gattCharacteristics)
+        : undefined;
+    this.manufacturer = manufacturer;
+    this.model = model;
+    this.firmwareVersion = firmwareVersion;
+    this.serial = serial;
+    this.reconnectOnDisconnect = Boolean(reconnectOnDisconnect);
+    this.requiresPairing = Boolean(requiresPairing);
+    deepFreeze(this);
+  }
+
+  merge = (partial) => new Core(Object.assign({}, this, partial));
+}
diff --git a/js/device/capabilities/cyclingPower.js b/js/device/capabilities/cyclingPower.js
new file mode 100644
index 0000000..26443d0
--- /dev/null
+++ b/js/device/capabilities/cyclingPower.js
@@ -0,0 +1,17 @@
+import { deepFreeze } from "../../utils";
+
+export class CyclingPowerCapabilities {
+  constructor({ controlOpcodes = [], supportsCrankTorque = false } = {}) {
+    /*
+     * Если в конструктор передали ссылку на внешний массив,
+     * slice() возвращает новый массив. О бъект получает собственную копию,
+     * и дальнейшие изменения исходного массива снаружи не повлияют на
+     * this.controlOpcodes.
+     */
+    this.controlOpcodes = Array.isArray(controlOpcodes)
+      ? controlOpcodes.slice()
+      : [];
+    this.supportsCrankTorque = Boolean(supportsCrankTorque);
+    deepFreeze(this);
+  }
+}
diff --git a/js/device/capabilities/index.js b/js/device/capabilities/index.js
new file mode 100644
index 0000000..7433834
--- /dev/null
+++ b/js/device/capabilities/index.js
@@ -0,0 +1,5 @@
+import { Control } from "./control";
+import { Sensors } from "./sensors";
+import { Core } from "./core";
+
+export { Control, Sensors, Core };
diff --git a/js/device/capabilities/sensors.js b/js/device/capabilities/sensors.js
new file mode 100644
index 0000000..b1de6d2
--- /dev/null
+++ b/js/device/capabilities/sensors.js
@@ -0,0 +1,31 @@
+import { deepFreeze, isFiniteNumber } from "../../utils";
+import { validateCadenceQuality } from "../cadence";
+
+export class Sensors {
+  constructor({
+    supportsHeartRate = false,
+    supportsCadence = false,
+    supportsPower = false,
+    hrSamplingHz,
+    cadenceSamplingHz,
+    powerSamplingHz,
+    cadenceSourceQuality,
+  } = {}) {
+    this.supportsHeartRate = Boolean(supportsHeartRate);
+    this.supportsCadence = Boolean(supportsCadence);
+    this.supportsPower = Boolean(supportsPower);
+    this.hrSamplingHz = isFiniteNumber(hrSamplingHz)
+      ? Number(hrSamplingHz)
+      : undefined;
+    this.cadenceSamplingHz = isFiniteNumber(cadenceSamplingHz)
+      ? Number(cadenceSamplingHz)
+      : undefined;
+    this.powerSamplingHz = isFiniteNumber(powerSamplingHz)
+      ? Number(powerSamplingHz)
+      : undefined;
+    this.cadenceSourceQuality = validateCadenceQuality(cadenceSourceQuality);
+    deepFreeze(this);
+  }
+
+  merge = (partial) => new Sensors(Object.assign({}, this, partial));
+}
diff --git a/js/device/index.js b/js/device/index.js
new file mode 100644
index 0000000..9a3b639
--- /dev/null
+++ b/js/device/index.js
@@ -0,0 +1,66 @@
+import { Control, Sensors, Core } from "./capabilities";
+import { deepFreeze } from "../utils";
+
+const DeviceType = Object.freeze({
+  HEART_RATE: "heart_rate",
+  CADENCE: "cadence",
+  TRAINER: "trainer",
+  UNKNOWN: "unknown",
+});
+
+export class Device {
+  constructor({
+    id,
+    name,
+    type,
+    core,
+    sensors,
+    control,
+    connected = false,
+    lastSeen,
+  } = {}) {
+    if (!id) throw new Error("Device requires id");
+    this.id = id;
+    this.name = name || id;
+    this.type = type;
+    this.core = core instanceof Core ? core : core ? new Core(core) : undefined;
+    this.sensors =
+      sensors instanceof Sensors
+        ? sensors
+        : sensors
+          ? new Sensors(sensors)
+          : undefined;
+    this.control =
+      control instanceof Control
+        ? control
+        : control
+          ? new Control(control)
+          : undefined;
+    this.connected = Boolean(connected);
+    this.lastSeen = lastSeen;
+    deepFreeze(this);
+  }
+
+  withCore = (partial) =>
+    new Device(
+      Object.assign({}, this, {
+        core: this.core ? this.core.merge(partial) : new Core(partial),
+      }),
+    );
+  withSensors = (partial) =>
+    new Device(
+      Object.assign({}, this, {
+        sensors: this.sensors
+          ? this.sensors.merge(partial)
+          : new Sensors(partial),
+      }),
+    );
+  withControl = (partial) =>
+    new Device(
+      Object.assign({}, this, {
+        control: this.control
+          ? this.control.merge(partial)
+          : new Control(partial),
+      }),
+    );
+}
diff --git a/js/main.js b/js/main.js
index 2a16c51..f965458 100644
--- a/js/main.js
+++ b/js/main.js
@@ -1,5 +1,4 @@
 const startButton = document.getElementById("start");
-const FTM_SERVICE_UUID = "00001825-0000-1000-8000-00805f9b34fb";
 
 startButton.addEventListener("click", async () => {
   try {
diff --git a/js/utils/index.js b/js/utils/index.js
new file mode 100644
index 0000000..6f1a011
--- /dev/null
+++ b/js/utils/index.js
@@ -0,0 +1,14 @@
+const deepFreeze = (obj) => {
+  if (obj && typeof obj === "object" && !Object.isFrozen(obj)) {
+    Object.getOwnPropertyNames(obj).forEach((prop) => {
+      const value = obj[prop];
+      if (value && typeof value === "object") deepFreeze(value);
+    });
+    Object.freeze(obj);
+  }
+  return obj;
+};
+
+const isFiniteNumber = (v) => typeof v === "number" && Number.isFinite(v);
+
+export { deepFreeze, isFiniteNumber };