diff --git a/WaveshareUARTFingerprintSensor/Exceptions/SensorStateException.cs b/WaveshareUARTFingerprintSensor/Exceptions/SensorStateException.cs
new file mode 100644
index 0000000..aa0ccb5
--- /dev/null
+++ b/WaveshareUARTFingerprintSensor/Exceptions/SensorStateException.cs
@@ -0,0 +1,21 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace WaveshareUARTFingerprintSensor.Exceptions
+{
+    [Serializable]
+    public class SensorStateException : Exception
+    {
+        public const string SensorSleepingMessage = "Sensor is sleeping, can't send commands";
+
+        public SensorStateException() { }
+        public SensorStateException(string message) : base(message) { }
+        public SensorStateException(string message, Exception inner) : base(message, inner) { }
+        protected SensorStateException(
+          System.Runtime.Serialization.SerializationInfo info,
+          System.Runtime.Serialization.StreamingContext context) : base(info, context) { }
+    }
+}
diff --git a/WaveshareUARTFingerprintSensor/FingerprintSensor.cs b/WaveshareUARTFingerprintSensor/FingerprintSensor.cs
index 38dce9f..e87f1ff 100644
--- a/WaveshareUARTFingerprintSensor/FingerprintSensor.cs
+++ b/WaveshareUARTFingerprintSensor/FingerprintSensor.cs
@@ -10,6 +10,7 @@ using System.Threading.Tasks;
 using Unosquare.RaspberryIO;
 using Unosquare.RaspberryIO.Abstractions;
 using Unosquare.WiringPi;
+using WaveshareUARTFingerprintSensor.Exceptions;
 
 namespace WaveshareUARTFingerprintSensor
 {
@@ -32,6 +33,7 @@ namespace WaveshareUARTFingerprintSensor
         private readonly int _rstPinNumber;
         private IGpioPin _wakePin;
         private IGpioPin _rstPin;
+        private bool _sleeping = false;
         private readonly object _lock = new object();
 
         public FingerprintSensor(string portName, int wakePin = 23, int rstPin = 24)
@@ -75,6 +77,11 @@ namespace WaveshareUARTFingerprintSensor
 
         private (byte first, byte second, ResponseType responseType) SendAndReceive(CommandType commandType, byte first, byte second, byte third, int timeout = DefaultTimeout)
         {
+            if (_sleeping)
+            {
+                throw new SensorStateException(SensorStateException.SensorSleepingMessage);
+            }
+
             // Command packet
             byte[] buffer = { PacketSeparator, (byte)commandType, first, second, third, 0, 0, PacketSeparator };
 
@@ -170,11 +177,13 @@ namespace WaveshareUARTFingerprintSensor
 
         public void Sleep()
         {
+            _sleeping = true;
             _rstPin.Write(GpioPinValue.Low);
         }
 
         public void Wake()
         {
+            _sleeping = false;
             _rstPin.Write(GpioPinValue.High);
         }