If Google keeps answering your searches with "Our systems have detected unusual traffic from your computer network", the CAPTCHA is not judging you. It is judging the IP address your searches leave from. That one detail explains most of the behaviour that makes it feel random.
Three things that follow from "it is per IP"
Signing in does not exempt you, and clearing cookies does not reset it. Everything leaving your network through the same public address is judged together, including your phone, your colleague's laptop and the browser extension you forgot about.
Solving it does not fix it. The CAPTCHA lets one search through. Whatever sent the automated-looking traffic is still sending it, so the next search trips it again.
The page tells you which address it is judging. It prints the IP near the bottom. If that is not the address your router or phone reports, you are behind a VPN, a proxy or a carrier that shares one address between many customers, and that is the first place to look.
A five-minute way to find the cause
- Switch network (Wi-Fi to mobile data or the reverse). If it stops, the cause belongs to the network.
- Turn the VPN off. VPN exit addresses are shared by thousands of people, some of them running scrapers. This is the most common cause there is.
- Open a clean browser profile with no extensions. If search works there, an extension is responsible: rank checkers, SERP exporters and some shopping add-ons query Google in the background.
- Compare devices on the same Wi-Fi. If only one is blocked, the cause is on that machine.
- Look at what you were doing. Fifty
site:searches in twenty minutes is exactly what the check exists to stop, whoever is typing them.
The part nobody likes to hear
If your address is shared, for example on mobile data or a carrier that puts many homes behind one IP, there may be nothing you can fix from your side. Someone else on that address is sending automated searches, and the CAPTCHA comes and goes on a schedule you cannot see.
And if the CAPTCHA appears during SEO work, such as checking a list of URLs for indexing by hand, the honest answer is that a browser is the wrong tool for that job and will keep getting blocked.
I wrote a longer version with a cause-by-cause table, what will not help, and the alternatives to checking by hand: Why does Google keep showing a CAPTCHA?
Have you hit a cause that is not on this list? I would like to hear it in the comments.
Disclosure: I build indexaction, a bulk Google index checker. The guide above is on its site.
