Would it be possible to create a solid beep like you would get with an active piezo buzzer using a piezo speaker instead? I'd like to use your 'differential drive’ technique to keep the higher volume. I played around with creating a new tone that was just a long note, but I wasn't able to get the sound I'm after. 

I am having an issue with battery drain. I traced it back to the rickroll song leaving power flowing to the buzzer after the song ends. 

It doesn't make any noise when connected to a passive piezo speaker, but when I connected it to a piezo buzzer, I hear a high pitched tone. I think that this means that there is power being sent to the buzzer, whether it makes noise or not, causing the drain. 

I haven't been able to find what caused this so far. I have attempted to add in a R note at the end of the song to see if that made a difference with no luck. I was wondering if you have run into this issue before.

EDIT: I managed to solve this by adding 

    digitalWrite(piezoPin1, LOW);
    digitalWrite(piezoPin2, LOW);

after the "for(int i = 0; i < (sizeof(melodyR)/sizeof(int)); i++){...} " section.

I added a melody: ‘here comes the bride’. Got my friends on their wedding night in the hotel room! Fantastic project, and the first I learnt to assemble off by heart :)

Nice. I like that you used a low memory use tune.

I pulled a similar thing on my girlfriend a few years ago. Unlike your elegant solution, I recorded a short phrase "hungry" and played that back when she walked by the fishtank. Same deal, sleep timer ATTiny85, mini JST battery but in a mini altoids tin with a PIR sticking out the side. There's just enough memory to play a short terribly digitized phrase hex encoded on the ATTiny85.. 

PIR sensor triggered the sound if it was awake at the right time. It would sleep a while but wake up quite often to try to catch someone walking by. The random bit was that it wouldn't trigger every time you walked by because it might not be awake at that moment, but every so often. Yours is definitely smaller and more consealable. I think I got several weeks of use before having to recharge. Always a hit, at least to the prankster. 

Good resource for ATTiny85 audio here: http://www.technoblogy.com/show?QBB

what a savage, i love it

I love it. Gotta try this out some time :-)

Oh, I'm so gonna make a couple of these and hide them in the IT department! 

Hah, that was you? Awesome.

It can be kinda risky to get caught planting electronic devices with power sources all around these days.

For rev 2, there's nothing wrong with getting a couple hundred manufactured and leaving them in a basket somewhere public with a sign that says "Free! Take one!"