Java/C++ PC Standby Detect and Prevent


This article shows how your Java (and C++) program can detect and refuse sleep/standby/hibernate requests made by the user or the system.


I wrote an application that is fed by a special PCI card, and runs 24/7. We found that if the PC went into standby mode, the PCI card was falsely activated, which was really bad. There was no easy way to uniformly disable the sleep/standby/hibernate features in Windows XP. Therefore, I decided to use the Windows API to detect whether a standby request is made and refuse it. Luckily, the Win32 API has a message, called WM_POWERBROADCAST, that is sent to all applications when the PC wants to go into standby or hibernate mode. The win32 subsystem will abort the standby if you return BROADCAST_QUERY_DENY from this message handler.

By using this API, the enclosed code is able to detect whether the computer goes into standby mode and, through the utilization of JNI, notify the rest of the Java code about that event. Also, the code lets you allow or disallow the PC to enter standby mode.

Using the Code

To use the code from Java, simply instantiate a StandByDetector object and provide the constructor with a reference to a StandByRequestListener. The listener will be notified when a standby/hibernate request is made on the PC. Use the setAllowStandby() to tell the code whether or not you want to allow entering a standby. Remember that the DLL (enclosed) has to be in your java.library.path path. Here is an example:

StandByDetector sd=new StandByDetector(new StandByRequestListener() {
   public void standByRequested() {
      System.out.println("standby requested");

To compile and run the demo:

  1. Extract the ZIP file contents into c:\temp, preserving the ZIP dir structure.
  2. Open cmd and cd into temp. Then, issue the following on the command line:
  3. javac com\ha\common\windows\*.java 
  4. Then, to run the demo, issue on the command line:
  5. java -Djava.library.path=C:\temp\com\ha\common\windows -classpath
  6. Now try to put the PC in standby: Task manager->Shut Down->Stand By.
  7. You will note that the cmd shell shows the message "standby requested" and the PC does not go into standby.



  • 64bit library

    Posted by thomas on 01/12/2017 10:10am

    I don't get the library compiled, could you upload a 64bit version?

  • PC Standby mode in windows 7

    Posted by xyz on 01/20/2014 08:36am

    Does this works on windows 7. I tried downloading and using the code on my laptop having windows 7. I get a dialog box. But when i put the laptop to sleep mode . It goes to sleep mode. How do i test this on windows 7 laptop or it would be of great help if i let to know if any changes are required to be done. Thank You

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