This story is available exclusively to Insider subscribers. Become an Insider and start reading now. The US wants VCs and founders to blow the whistle on suspicious investments in American tech firms. The Committee on Foreign Investment in the US created a "tip line" in the summer. But VCs' and techies' unawareness of it poses a challenge to efforts to block China from US tech. For an informant calling in with a hot tip about a national security threat, the generic voicemail greeting provides little sense of urgency. Without introduction, a man's voice says "the Office of Investment Security and Committee for Foreign Investment in the United States." That is followed immediately by the ubiquitous prerecorded greeting of "is not available. Record your message after the tone."