If you’re after some free software to alert you when there is dead air, then Pira.CZ has a solution for you. Their freeware silence detector software is very flexible, and I highly recommend it. I’ve used it for several stations, sending alerts as emails, SMS messages and phone calls.

Setup is easy. Install it on your Windows computer, select an audio source, set a threshold, and configure your alerts. Here are some of the alerts I’ve setup:

SMS Alerts

I have an account with SMS Global, and use their Email to SMS feature in order to send SMS messages to my phone. This was particularly useful before I got a smartphone, but I don’t rely on it so much any more.

Phone Calls

UPDATE April 2017: You can now easily trigger phone calls via Twilio!

Using a plain old dialup modem, you can have your phone ring automatically. In instances where I’ve set this up, we have a dedicated PSTN line (usually from an ADSL connection or backup lines for your VoIP system) used solely for this purpose. That way whenever I receive a call from that number, I know it’s a PFA.

The way to set this up is to send a command to the serial port your modem is connected to. The commands are usually in the format “ATDT0299991111” (where those last 10 numbers are the phone number). I use the Pira.CZ software to trigger a VBScript, which then in turn opens PuTTY and sends the command to the modem. Here is that script:

set WshShell = WScript.CreateObject(“WScript.Shell”)
If Wscript.Arguments.Count > 0 Then

WshShell.Run “C:putty.exe -load COM1 ”
WScript.Sleep 1000
WshShell.AppActivate “HOSTNAME – PuTTY”
WshShell.SendKeys “ATDT”
WshShell.SendKeys Wscript.Arguments(0)
WshShell.SendKeys vbCrLf
WScript.Sleep 1000
MsgBox(“No phone number passed. Could not dial.”)

End If

Within PuTTY, I have a connection preset called “COM1” which connects to the serial port. This VBS accepts an argument (which is the phone number).The Pira.CZ software is also setup to terminate PuTTY when audio resumes.

Backup Audio

If you don’t have a dedicated emergency program player installed, you can use this software to play a MP3. This will play out the main soundcard, so unless you can control a router to switch audio sources you’ll need to run this on a computer which is always active on your program feed.


This software is highly flexible and can be used for a variety of things. I’ve only scratched the surface here by writing about the featured I’ve used in the past.