One of the shinest features in WiFi networking, this year, is routers with dual LANs. One LAN provides access to the Internet, and all computers to each other, like a normal router. The second LAN provides access only to the Internet.
You connect all of your personal computers to the first LAN. When you have guests, they can bring their personal computers, connect to the second LAN, and surf the Internet without having any access to your personal computers.
You can even lower the security level on the "Guest LAN" to accommodate your guests, without exposing your personal computers to abuse by possibly malicious neighbours. Or possibly, to your guests computers themselves - which may not be secured to satisfy your personal standards, and may have malware infestations.
Virtual LANs, or "VLANs", used to be features available only on advanced, enterprise grade networks. With computers being a common item in the home, simple VLANs (multiple LANs provided by a single router) are now available to Small Office / Home Office ("SOHO") networks.
Last year, if you wanted equivalent protection for your home computers, you'd be advised to buy 3 routers. You would connect one router directly to the modem, and connect the other 2 routers to the first router as peers. One of the secondary routers would provide your "Personal", secure LAN; the other, the "Guest", less secure LAN. This arrangement, while providing more security for your computers, will have disadvantages.
- Complexity. Three routers will require more cabling, and more physical space than one router.
- Cost. Three routers are going to cost more than one router.
- Networking side effects. Look up discussions about "double NATting", for more about this problem.
A modern, dual LAN router has none of the latter disadvantages, just improved security for you, and increased convenience for your guests.