How hard would it be for somebody on my home wifi network to get all the data coming in and going out, even data sent by other computers?

For someone to intercept and access all the data coming in and going out of your home Wi-Fi network, including data sent by other computers, several factors and methods come into play. Here are some key points to consider:

Encryption

If your Wi-Fi network is not properly encrypted, it becomes much easier for an attacker to intercept data. Using outdated encryption protocols like WEP or even WPA is not secure. It is crucial to use the latest encryption standards such as WPA3 or at least WPA2 to protect your network25.

Network Access

An attacker who gains access to your network, either by cracking the Wi-Fi password or through other vulnerabilities, can potentially intercept data. This can be done through various methods such as setting up a rogue access point (e.g., an "evil twin" attack) or exploiting weaknesses in the network configuration45.

DNS Interception

Even if the network is encrypted, there is a risk of DNS interception, where the router or another device in the network redirects DNS queries to a different resolver. This can happen transparently and may not be easily detectable. However, this typically involves modifying the DNS queries rather than intercepting all data traffic3.

Passive Listening

Advanced techniques, such as those described in the University of Chicago study, involve passive listening to Wi-Fi signals to detect motion and occupancy. While these methods do not intercept data directly, they highlight the vulnerability of Wi-Fi signals to external monitoring. However, intercepting actual data would require more active measures1.

Securing Your Network

To protect against data interception:

• Ensure your network is encrypted with WPA3 or WPA2.
• Change default router settings, including the admin password and network name.
• Keep your router software up to date.
• Disable features like WPS, UPnP, and remote management.
• Use a firewall and maintain antivirus software.
• Set up a guest network to isolate visitors from your main network25.

In summary, if your network is not properly secured with strong encryption, updated software, and secure configurations, it can be relatively easy for someone on your network to intercept data. However, with proper security measures in place, the risk of such interception can be significantly reduced.