Android/ios/Mobile : How can we "SECURELY" do bluetooth pairing without prompting anything on user screen?

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http://stackoverflow.com – I know we can pair any bluetooth device without promoting on user screen but it is not secure. I guess as passkey will remain same for such connections for all the devices so anyone can sniff or do eavesdropping. How can we reduce the risk or make it more secure? I heard somebody is saying user public/private key to generate the link key but is that possible for such insecure connections?? Ref Secure Simple Pairing I hope I am able to put the question clearly ! (HowTos)