Scanning for Peripherals

Once the CBCentralManager is up and powered on, you can create a function that scan for peripherals around us.

Create a function called startScanning. Call the method scanForPeripherals(withServices:).

This method scans for peripherals that are advertising services. Now since the unique identifier is set up, add that reference to the method.

func startScanning() -> Void {
  // Start Scanning
  centralManager?.scanForPeripherals(withServices: [CBUUIDs.BLEService_UUID])

Now add the startScanning() function to the centralManagerDidUpdateState to scan as soon as the app opens.

extension ViewController: CBCentralManagerDelegate {

  func centralManagerDidUpdateState(_ central: CBCentralManager) {
     switch central.state {
          case .poweredOff:
              print("Is Powered Off.")
          case .poweredOn:
              print("Is Powered On.")
          case .unsupported:
              print("Is Unsupported.")
          case .unauthorized:
          print("Is Unauthorized.")
          case .unknown:
          case .resetting:
          @unknown default:


When you run your app, your device will start scanning for peripherals.

Discovering Peripherals

Now that scanning is started, what happens when a peripheral is discovered?

Every time a peripheral is discovered, the CBCentralManager will notify you by calling the centralManager(_:didDiscover:advertisementData:rssi:) function on its delegate.

This function provides the following information about the newly discovered peripheral:

  • The discovered peripheral is recognized and can be stored as a CBPeripheral.
  • The discovered peripheral has stored advertisement data.
  • The current received signal strength indicator (RSSI) of the peripheral, in decibels.

Since you are interested in connecting to one peripheral, create an instance of a peripheral.

private var bluefruitPeripheral: CBPeripheral!

Call the didDiscover function. This tells the delegate the central manager discovered a peripheral while scanning for devices.

func centralManager(_ central: CBCentralManager, didDiscover peripheral: CBPeripheral,advertisementData: [String : Any], rssi RSSI: NSNumber) {

    bluefruitPeripheral = peripheral

    bluefruitPeripheral.delegate = self

    print("Peripheral Discovered: \(peripheral)")
  	print("Peripheral name: \(")
    print ("Advertisement Data : \(advertisementData)")

The implementation of this function performs the following actions:

  • Set the bluefruitPeripheral variable to the new peripheral found.
  • Set the peripheral's delegate to self (ViewController)
  • Printed the newly discovered peripheral's information in the console.
  • Stopped scanning for peripherals.

Next up - actually connect to that peripheral.

This guide was first published on Jul 27, 2017. It was last updated on Mar 08, 2024.

This page (Scanning for Peripherals) was last updated on Mar 08, 2024.

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