The UK has been experiencing record-breaking temperatures, hitting 99.1°F/37.3°C, which is not only dangerous for vulnerable populations but also hard on infrastructure like power and phone lines. Cables expand, sag, and cause outages - exactly what's been happening. The author's power station has seen more action in the past few days than all winter, and they expect this to continue.

To keep their home internet running when the phone line goes dead (they already have a Starlink dish, but that's for a different scenario), the author explored three methods to connect an old Android phone to their router as a backup. The first method uses a USB cable: plug the phone into the router's USB port, enable USB tethering in settings, and many routers will auto-detect it as a WAN connection. Budget routers may not support this, but third-party firmware like OpenWrt or DD-WRT can help.

The second method uses the phone's Wi-Fi hotspot but keeps the router as the main router - this requires the router to support WWAN (Wireless Wide Area Network). Few routers do, but travel routers from GL.iNet (like Beryl AX, Slate 7, Mango) and some Draytek or Ubiquiti UniFi models support it. Again, OpenWrt or DD-WRT can enable this feature on compatible routers.

The third and best method uses a USB-C-to-Ethernet adapter. Connect the adapter to the phone, plug an Ethernet cable from the adapter to the router's WAN port, then enable Ethernet tethering on the phone. This works with virtually any router that has a WAN port. Stick to adapters from reputable brands (Anker, Ugreen, Plugable) in the $10 - $20+ range, especially those with ASIX AX88179 or Realtek RTL8153 chipsets.

One catch: the phone won't charge via Ethernet tethering, so you'll need to schedule downtime for charging or use a USB-C multi-port hub with power delivery. For iPhone users, USB tethering works only if the router supports Apple's proprietary protocol; Wi-Fi tethering works if the router supports WWAN; and Ethernet tethering is a no-go. An old Android phone with a data SIM is the recommended solution for reliable backup internet.