High pitched beep in house every 15 minutes
The only thing I have ever heard of making the high pitched beep at intervals is fire or house alarms.  If you have a dead battery in your fire alarm it will go straight to its backup power and beep.  Given the pitch and the proximity to the ceiling and how well the sound echoes it can drive you nuts.  

The thing is most of the time these alarms are all installed at the same time.  So if you try to figure out which one it is and which battery to replace, well you are doing the same thing a week from now.  And we all know that batteries only die between 1-6 AM.