Wednesday, October 3, 2007

Eavesdropping on ooma calls


When a call is routed through someone's Hub and onto their phone line, it is a rather simple matter for them to eavesdrop on the call. Ooma continually claims that they have "proprietary" technology to detect and/or prevent this, but that appears impossible, since a circuit, such as that shown at right, can easily be constructed which is undetectable.

Ooma claims to have a "proprietary" solution to this problem, but all techncial experts suggest that the most the Hub could do is to detect the drop in voltage across the line if another phone directly connected to the line goes off hook, and then break the connection in the Hub. (This is exactly what an answering machine does, so it is hardly new or "proprietary".)

If one wants to do eavesdropping on the calls going through their own phone line (maybe to make sure that no one is using it for illegal purposes for which the subscriber of the line will be held responsible) all they have to do is connect a simple circuit which presents a high DC-impedance across the line and the Hub can not possibly detect its presence. The circuit is shown, where the values of the capacitors and matching transformer depend on the nature of the input to the amplifier. Use at your own risk.

Or try the inductive tap circuit described at Unterzuber.

A more complicated (but perhaps a lot more interesting) way to capture calls made by the ooma hub on behalf of other omma subscribers would be to connect the ooma hub to an Asterisk box with an FXO/FXS card, or perhaps a Linksys/Sipura 3102 or other ATA with FXO and FXS ports (or a Sipura plus a Trixbox). The Sipura/Asterisk box could pass the call through while recording it - this would be totally transparent to the Ooma box. I will try to provide a full how-to for this in a future post.

As an ooma user, to prevent others eavesdropping on your calls in this manner, prefix all calls made via the ooma network with *82 - this also has the added benefit of presenting Calling Line ID to the callee, so that your friends who screen their calls will answer.

1 comment:

Mike Pierce said...

Thank you for copying the stuff on Ooma that I had posted earlier. Glad to see it available after I removed the web site under threat of legal action and didn't want to spend the time to revise it. Good luck bringing the truth to the potential users.