The VS-100 sensor looks for between 3-25 volts. You can use any number of Xantech sensors to accomplish what you need.

[Link: xantech.com]
[Link: xantech.com]
[Link: xantech.com]

If the device still draws too much power in standby, you can use the SMLIT01 on the PC's power light.

[Link: remotecentral.com]