Best transducers according to redditors

• Fire TV Stick, which is a lower-cost alternative to the awesome Fire TV. (think Apple TV, but actually good)
  
  
• Raspberry Pi which is a tiny fully-functional/fully-featured ARM computer.
  
  
• Arduino, which is an easy-to-use electronics prototyping platform, great if you're interested in learning how to make your own electronics and whatnot. (you might also want this, this, this, this, and this. Should be less than $40 altogether, though you could also probably find like a starter kit that comes with an arduino, book, and components.)
  
  
• Huion drawing tablet, great for if you want to do digital art. I haven't used this model specifically, but I do have the (bigger/more expensive) Huion 610 Pro, which I love.
  
  
• Amazon Prime student was like $40 IIRC, not sure if that has changed though.

I think that's a standard buzzer.

https://www.amazon.com/Uxcell-a15112300ux1631-Electronic-Electromagnetic-Continuous/dp/B01ARBOT9Y/ref=sr_1_3?s=industrial&ie=UTF8&qid=1485038861&sr=1-3&keywords=buzzer

The MK133 kit will do the job pretty well.

You can add just about any arcade button you like to the MK133. Just wire them in parallel with the on-board pushbutton switches.

Here is a busser that should work with the MK133. Unfortunately it'll sound off continuously until the Reset button is pressed. To make it do a short beep instead will require a little more work.

GPIO doesn't output hardly anything in terms of power, so you'll likely want at Class D amp to go with it, if you want anything approaching "loud". Could probably power a buzzer via GPIO that would be "loud" if you're right next to it, but "loud" from across a house? You'll need an amp and a buzzer, and probably a case to put them in, and something to power the amp...

Surely you could toss something together for less than $40 to do this, but the Aeotec is also a Z-wave repeater, which if you're using Z-wave devices (and if you're using Home Assistant, presumably you are), so it's overall a decent enough value.

The GPIO have a max of 16mA per pin, and that's really pushing it. If you want long life out of your board, the max is recommended at 3mA per. Let's just say you run at 16mA, at 5v that's 0.08 watts, which is not a whole lot...

Even something like this not-at-all-loud and tiny piezoelectric buzzer is too much amperage: https://www.amazon.com/BQLZR-Continuous-Buzzers-Computers-Printers/dp/B00J4BJZP2

You'll pretty much have to add a small class D power amp if you want to drive anything loud (100+ dB).

The Combustion course threw me - I was thinking you were trying to make a dyno - with electric motor used as a generator.

If you just want to measure power in a single phase AC motor - as I mentioned a transducer - does your NI system have 0-5V analog inputs? Try this -> http://www.amazon.com/dp/B005CWN8U0/ref=biss_dp_t_asn

You want something like this:

https://www.amazon.com/CR-Magnetics-CR8401-1000-General-Transformer/dp/B005CWO8GI/ref=pd_sbs_328_26?_encoding=UTF8&refRID=3KT0G435SVH789VEDQR6&th=1

Or this:

https://www.amazon.com/bayite-Digital-Current-Voltage-Transformer/dp/B01DDQM6Z4/ref=sr_1_1?ie=UTF8&qid=1487698916&sr=8-1&keywords=current+sense+monitor

5 buzzers for under 5 bucks. Doesn't do the different pitches like a discovery will, but does me fine on my Naze. https://www.amazon.com/dp/B00B0Q4KKO/ref=cm_sw_r_cp_apa_qgJvxb1SCKMV6

I've been using these.

They're not "ear piercing", but annoyingly loud, and lets me find my quad within 100-150 feet in grass even with moderate wind noise and traffic nearby. I'd say they're about 60% of the loudness of a normal smoke alarm, if that gives you any idea.

i bought me a pack of piezo buzzers and have slapped them on a few of my kwads. Tied to a switch, and it's LOUD as all hell.

another method i've heard is.. you flatten out your remote antenna and start waving it left to right parallel with the ground. when the signal drops, this is supposed to indicate the antenna is pointing to the kwad. walk forward five feet and repeat.