I use alarms and I set alarms for my breaks too. I try and stick to them exactly. I have also found that pomodoros create unnatural stopping and starting points. If alarms don't work for you, it might just be about structuring your time, like getting the ting that you want to do the least out of the way first and just finishing it however long it takes? This is a good question though... I am not sure what the best stratagey is for pomodoros without an alarm system!