Google Tone is a free Chrome extension which allows you to send and receive links via audio tones.

Install the extension and it adds a button to your address bar. When you're at a page you'd like to share, click the button and Google Tone encodes the URL and plays it as around two seconds of audio tones.

Anyone close enough who's also running Google Tone should receive a notification saying you're sending them a link (depending on your audio volume, background sound levels etc). If they're interested, clicking this opens the page in a new tab.

Google Tone worked for us, most of the time. And it's good to see that it can both send and receive links (the similar Chirp extension can only send).

As often with Google, though, there are privacy concerns. You must log in with your Google account before the extension will work. It also "temporarily stores a URL on Google's servers" before sharing it, and "collects anonymous usage data in accordance with Google's privacy policy".