I have an old serial based remote control for the PC. It has an IR receiver that plugs into a standard DB9 serial port. I am trying to figure out how this remote works. I have downloaded various serial monitor programs to try and figure out how it works. However, none of them display anything when I point the remote control at the receiver and press buttons. I know the remote and receiver work. Maybe I am doing something wrong. Any help with this would be greatly appreciated.
Sometimes devices like that use pins like DTR (Data Terminal Ready) which trigger an interrupt and track the time between interrupts and decode that rather than actually feeding data in to the serial port on the data lines.
(edit: The software might be polling a line in software rather than relying on a port to have something interrupt on one of the pins. DTR and RI, ring indicator, are still the likely suspects. Power to the device, likely an IR phototransistor, is likely to be from driving one or more of the extra pins to +12v. See: http://www.tldp.org/HOWTO/Serial-HOWTO-19.html)
As BitShifter said, the device might be using some pins other than Transmit/Receive, so a software monitor might not detect much. The best you can do is get a hardware device with LEDs like this
which i found on http://www.awrtech.co.uk/awr_cat.htm (look for RS232_SPM) that shows you which of the lines do something while your device is active. After that, you might be able to monitor the relevant pin in software, or use a scope or a logic analyzer to find out what's actually going on.