Wi-Fi is great - except when it isn't. Aside from the obvious security problems and making sure your network is locked down, you also need to deal with Wi-Fi range problems.
It always seems that there is one critical room or office that is just beyond the reach of the Wi-Fi signal emitted by your wireless router or access point. And if you have one of the "gateway" all-in-one (modem/router) devices supplied by many Internet Service Providers, the problem could be worse. Those devices often have anemic Wi-Fi range.
A very simple solution is to use PowerLINE networking to extend the range of your network. Netgear makes a relatively inexpensive and simple kit that includes two devices. Each simply plugs into your home or office electrical outlets. The "sending" end has an Ethernet port for connecting to your router. The "receiving" end has a built-in Wi-Fi access point to broadcast your Wi-Fi signal to a room or office that is beyond the reach of your main wireless router or access point.
The kit is called the Netgear PowerLINE Wi-Fi 1000 - Essentials Edition PLW1010-100NAS. It has been on sale at Amazon for $80, but usually sells for $100. At either price, it is an inexpensive and "plug and play" solution to extending your Wi-Fi network.