GetSignalStrength.cs

public IObservable<float> GetSignalStrength()
        {
            return Observable.Create<float>(observer =>
            {
                var centralManager = new CBCentralManager(DispatchQueue.CurrentQueue);

                centralManager.DiscoveredPeripheral += (object sender, CBDiscoveredPeripheralEventArgs e) =>
                {
                    observer.OnNext(e.RSSI.FloatValue);
                };

                centralManager.FailedToConnectPeripheral += (object sender, CBPeripheralErrorEventArgs e) =>
                {
                    observer.OnError(new Exception("Failed to connect to device"));
                };

                return Disposable.Empty;
            });
        }