Very few of our signals are strong enough to stand out above the noise for any but the nearest distances, and those have not been consistently transmitted for very long. It may be physically possible to pick up the Dew Line or I Love Lucy reruns for a couple of hundred light years, but a listener would have to be very lucky to be tuned in at the right time, place and frequency. We've only had radio of any kind for about a century, and it's highly unlikely ETI has or will pick up what we've transmitted so far. The galaxy is a noisy place at microwave freqs, and unless ETI knew exactly what and where he was looking for, it's unlikely he would have heard us so far. This is not a technology issue, it's an SNR issue. It may be possible for them to know we're here, but that doesn't mean it's probable. Besides, I would suspect ETI search strategies are optimized to scan for deliberate "Hello, I'm over here" beacons. They would never guess we were smart enough to be quiet and still stupid enough to let stray radiation leak out.

This may not always be the case, but for the time being we're probably safe. It's like lighting a cigarette on a nighttime patrol...not a smart thing to do, but chances are you'll get away with it, at least for a little while. You also have to keep in mind, alien tech may be capable of easily picking us up, but that doesn't mean they've necessarily bothered to deploy it. After all, we've got the technology right now to employ a pretty effective passive SETI program, but we haven't bothered to do so. They may have given up centuries ago after thousands of years of listening in our direction.