Whether you don't want to keep your home lab computers on 24/7 for security reason or just want to be environmentally friendly and save energy, you want to be able to switch on/wake up your computer on demand.
The popular way to achieve this is utilise WoL - Wake On Lan, an old technology back in 1997. Basically you can turn on your computer from anywhere. It involves configure your Router, set up a DDNS and turn on WoL BIOS features. We won't discuss details here today, rather, we target the computers that do not support WoL in their BIOS.
There is actually a option before my experiment - Remoteboot with ESP8266 chipset, but it aims to Desktop PC only, not Apple computer or laptops, because it requires standard power and reset interfaces - means you need to plug pin into the mainboard. Anyway, it might still be an option for you and you can visit here for more information: https://www.kickstarter.com/projects/658903329/remoteboot-wifi-remote-management-module-for-pcs/description
Well if your BIOS not support WoL you might still be able to wake up it by using a very simply technique - shake your mouse. I'm not kidding.
Wireless mouse is preferable, you should at least set up your computer waking up by keyboard/mouse. Go to Power options on your Windows/Linux machine. Most mouse should work but if it does, just try another mouse. One of my Logitech wireless mouses doesn't work, experiment it.
After getting your mouse working and waking up while it's sleeping here is the real work, but still, you need at least one equipment to get it work - an old mobile that can vibrate on incoming calls plus a SIM card(this card should be able to take phone calls), then put your mouse over the mobile.
When your computer is in sleep mode, ring the number from anywhere, your computer will be waking up. No DDNS setup, no need to mess up with your router, and no need raspberry pi as medium inside LAN, no need another computer as medium inside your LAN if you use Teamviewer or logmein.
If you find the vibrate is not strong enough to wake up your computer, put a pen under the mobile, try again.