WOLDroid is a Wake On Lan application, that can turn on computers supporting this feature. (All newer computer has this feature) You can find several WOL applications, but WOLDroid stands out with the feature to detect if a computer is on. For each computer you can specify an IP address (or name) and a port. If WOLDroid can connect to this address and port, it will show the computer as on. WOLDroid has both WAN and LAN settings for each computer, so you can turn on a computer from the WAN side if have your router set up to allow it.