preventing battery drain when no connection??

Two things:
1) it sounds like you could also turn off sync to prevent the phone from trying to update
2) sounds like tasker MIGHT be able to do what you want

 

Couldn't he do this with Tasker? It's not like he's asking it to stay in airplane mode until it detects a signal (impossible, as you say), he just wants it to go to airplane mode for 15 minutes, spend 5 minutes out of airplane mode, and if no signal is found go to airplane mode for 15 minutes again.

There's probably an app for it, but what kind of search would you use to find it? Everything I can think of brings up all kinds of stuff that's not quite right.

 

You should be able to do this pretty easily with a powerful tool, like Tasker.

I think you can even do it with the less powerful but (free, open-source) Llama (which is what I use) by having the phone go into airplane mode after X minutes of no-service, and then waking up every Y minutes to check for service. I just created such an "Event" in Llama but I don't really have an easy way (nor the time) to test it. In Llama, I think the instructions would be as follows for this "Event".

Conditions (to select):
1) "Mobile data not connected".
2) "WiFi not connected".
Then select "Advanced..." and check "Delay event" and choose the amount of time (e.g. 5 minutes) that you want the phone to wait before going into airplane mode. Also check "Cancel delayed if false". That way the phone will only to into airplane mode if you lose service for 5 straight minutes.

Actions (to take):
1) "Toggle Airplane Mode On".
2) "Queue another event". (E.g. Call it "Sniff for service".) Select the desired Queue delay (e.g. 15 minutes) with an "Action" of Toggle Airplane Mode Off".

The result should be as follows (I think). Any time you lose a data connection (cellular AND WiFi) for 5 minutes straight, the phone goes into airplane mode but the phone wakes up every 15 minutes to sniff for service and goes back down after 5 more minutes of no service.

There might be several other solutions through Llama since you can have Llama take certain actions based on your proximity (or lack thereof) to certain cell towers.

FYI: My phone not only burns through batteries if it loses its cellular connection, but it also burns through batteries if it's even roaming. (My Sprint plan has free roaming onto Verizon, and I'm sure Sprint has to pay Verizon for the minutes/data so I guess Sprint programs their phones to work like crazy to get off of Verizon's service ASAP.) If I turn roaming off, I can save some juice when I'm outside of Sprint coverage. Also, somebody hacked an app that is specific to my LG Optimus S phone which lets me lock the phone into roaming-only mode thereby saving juice if I'm in an area with Verizon service but not Sprint service.

 

I see. I (and I think the others) were thinking you'd just stick it in airplane mode before going somewhere with spotty coverage, rather than waiting for coverage to drop.

How about something that plays a notification sound when you lose/gain connectivity? I vaguely remember something like that (except of course with a simple beep) being common in the early days of cell phones, or maybe it was something else that depends on a spotty signal...

 

Gorlash: Try the Llama solution that I described above. It should do exactly what you want.