When a company adopts Stripe, Intercom, HubSpot, or Calendly, nothing announces it. No press release, no changelog entry a stranger can subscribe to. The only public trace is a script tag on a page - assuming that tag shows up in a way anyone's actually watching for.
Buying Signal Watcher tracks a list of company domains on a schedule and reports only what's new since the last check - a new tool showing up means a company just adopted (or dropped) a piece of stack you're watching for, not a full inventory replayed every run. It renders each page like a real browser, so it catches tags injected client-side, not just what a static HTML fetch would see.
That rendering choice came from testing, not a guess: against 6 real company sites (close.com, gumroad.com, buffer.com, clearbit.com, loom.com, zapier.com), a plain HTTP fetch - the cheap, standard way to check a page - found a detectable tool on only 1 of 6. The rest load their tags through Google Tag Manager, which injects scripts client-side after the page has already loaded; a static fetch never sees them. Switching to real browser rendering (Playwright) caught 4 of 6.
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