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The short answer: if you want to keep smart-home gadgets away from your laptops and phones, use your new router’s guest network. An old router is better for two other jobs: running a separate 2.4 GHz network that fussy gadgets can join, or carrying your Wi-Fi to a far-off room. Either way, only reuse a router that still gets security updates.

Here’s what to check first, the three setups and what each one is really good for, and a safety checklist for the old router.

Why gadgets need special care

The National Institute of Standards and Technology (NIST) points out that a smart doorbell might be more easily hacked than a computer holding your financial records. That’s why it suggests keeping smart-home devices on a separate network.

There’s a practical reason too. Many smart-home devices only work on the older 2.4 GHz Wi-Fi band, not the faster 5 GHz one. Google and Apple both say some devices won’t connect to 5 GHz. 2.4 GHz also reaches farther through walls.

First, check what you have

  • Is the old box rented from your internet company? Then it has to go back to them, not into a new job.
  • Is it a modem and router in one box? Those often can’t work as a second router. A plain router with an “Internet” or “WAN” port is what you want.
  • Does it still get updates? Check before you go further. Here’s how to tell if your router is too old.

Three setups, and what each is good for

1. For security: your new router's guest network

Most routers can run a second “guest” network with its own name and password. The Cybersecurity and Infrastructure Security Agency (CISA) recommends putting smart-home devices on it if they only need internet access, because that stops them from finding your other devices. No old router needed.

The catch: guest networks often block devices from talking to each other. That can break casting to a TV, or a smart speaker controlling your lights. If something stops working after you move it, this is the likely reason.

2. For fussy gadgets: the old router as a separate network

Plug a cable from the old router’s Internet (WAN) port into a regular port on your new router. The old router then runs its own Wi-Fi network. You can set it to 2.4 GHz only, give it a clear name like “Home-Gadgets,” and connect gadgets that struggle with your main network.

This is not a security fix. It blocks traffic coming in from your main network, but a hacked gadget behind the old router can still reach your computers. It also splits your home in two. Apple says your phone, accessories and home hubs must be on the same network, and Google notes devices on separate networks “can have a hard time communicating.” So any speaker or hub that controls these gadgets has to join the gadget network too, or automations and voice control may stop working. Netgear and Google add that a router behind a router can cause problems with online gaming and VPNs.

3. For coverage: the old router as an access point

In “access point” mode, the old router stops acting like a router and simply extends your main network. That’s handy for a far-off room or a garage. Connect it to your new router with a cable and turn on access point mode in its settings.

Which port to use depends on the brand, so follow the maker’s guide below. This adds coverage, not separation: your gadgets end up on the same network as everything else. ASUS notes its firewall is off in this mode, and TP-Link says its guest network is no longer kept separate.

Before you plug it back in: a safety checklist

Work through these in order:

  1. Reset it so you start clean. Here’s how to reset your router, brand by brand.
  2. Update its firmware, the router’s built-in software, from the app or settings page. If the maker no longer offers updates, stop here and retire it. The FBI warned in 2025 that criminals are taking over end-of-life routers. Here’s how to get rid of an old router safely.
  3. Use WPA2 or WPA3 security, the settings that scramble your Wi-Fi. The FTC says older WEP and WPA settings aren’t secure.
  4. Change the admin password from the default.
  5. Turn off WPS and remote management. WPS is a push-button shortcut for joining Wi-Fi, and remote management lets the router be controlled over the internet. The FTC and CISA both recommend turning them off.
  6. Consider turning off UPnP, a feature that lets devices open connections through the router on their own. The FTC recommends turning it off. But casting devices like Chromecast rely on it, so if casting stops working afterward, this is the likely cause.

Setup tips that save headaches

  • Turn on 2.4 GHz on the gadget network, since that’s what many smart devices need.
  • Set up devices with your phone on the same network they’ll use.
  • If you can’t reach the old router’s settings page after connecting it, the two routers may be using the same address. Give the old one a different address in its settings, as TP-Link’s guide describes.
  • Thread gadgets work differently. They connect through a “Thread border router” rather than straight to Wi-Fi, so they don’t need the old router. Some Wi-Fi systems and smart-home hubs have one built in; check your device’s specs.

How to switch common brands to access point mode

  • Netgear: Advanced > Advanced Setup > Wireless AP, then choose AP Mode.
  • TP-Link: Advanced > Operation Mode (or “Change Mode” at the top right), then Access Point.
  • ASUS: Administration > Operation Mode > Access Point (AP) mode.
  • Linksys: Configuration > Connectivity > WAN Setup, then Bridge Mode.

Menus vary by model, so follow the maker’s guide linked in the sources. For help planning the whole setup, see our guide to creating a smart home network.

Common questions

What if my old router has no access point mode?

You can usually set it up by hand. TP-Link’s guide describes the steps for its routers: give the old router a different address and turn off its DHCP, the feature that hands out addresses, so the new router does that job alone.

Does the old router have to stay on all the time?

Yes, if any devices connect through it. Gadgets on its network, or in a room it covers, lose their connection whenever it’s off.

Sources