Accidental detection is nearly impossible with any foreseeable equipment.
The inverse square law makes detection of a spherically expanding signal supremely difficult, since the power received at interstellar distances would be infinitesimal. Look how bright even a giant star is at interstellar distances. Imagine how faint would be an artificial signal sent out spherically. If such a signal were beamed, it would be more likely to be detected. But the odds of capturing a beamed signal by pure luck are rather small.
I hold out no hope whatsoever of finding an unintentional signal. You might well disagree.