How do you know when someone is listening?<br><br>I'm not being facetious; there have been a number of cases where downed pilots have turned off their ELTs to "save the batteries", thereby prolonging the search. (Well, I know of one; I'm sure there have been others.)<br><br>The general rule for an ELT is:if you need immediate assistance (e.g. someone is badly injured), turn it on and leave it on. If you're not in imminent danger, turn it off until the SAR time on your flight plan (at which point you know the authorities will be starting to look for you), then turn it on and leave it on until (a) someone finds you, or (b) the batteries run out. <br>That supposedly gives you the best shot at being rescued if you know there's an organized search for you. Of course, a radio signal will carry much farther than a loud noise, so presumably, if they search party were close enough to hear the horn, you'd be able to hear them. Is that a reasonable assumption?