If there an easy way to determine if my washer and dryer are on with my arduino? I considered taking some wire and wrapping a few turns around the cords for each and then doing analogread off those wires but... Is there a better/easier way?
Is tweet-a-watt too expensive of a solution?
http://www.ladyada.net/make/tweetawatt/
I'd actually go for the inductance method, simple cheap and safe. That or something like a reed switch might work either next to the wire or there might be an electromagnet somewhere in the machine that turns on when it's on. Another option is hall effect sensors.
If you're really serious you could dig out the machines microcontroller and snoop around the pins, one of them should go to a relay to the power line.
Alec
How about fitting a light sensor over the ON light on the appliance?
I'd actually go for the inductance method, simple cheap and safe
I would also suggest a solution with a current sensor.
Example: http://www.nuvotem.com/en/products/as.shtml
With this solution you only need to mount the sensor over the power cable. Safe an easy.
How about fitting a light sensor over the ON light on the appliance?
Depending on the use, this may lead to a failure similar (in cause, not effect) to the Three Miles Island nuclear accident 
florinc - That'd work for the washer but not the dryer since the dryer doesn't run at 120. Also way more than I'd want to spend on this project.
Grumpy_Mike: neither device has an 'on' light.
Halabut, Webmeister - thanks! I will look into one of those sensors.
You may need something like this:
http://www.seeedstudio.com/depot/splitcore-current-transformer-wattson-compatible-p-519.html
Perfect! Thanks, florinc!
All the pictures of these I've seen in use require it to only be around one wire inside the power cord. Has anyone tried wrapping it around the entire power cord?
I'd like to do the same thing, but I don't have the option of cutting open power cables. My thoughts are either use this, or a vibration sensor to tell when the machines are running.
Looks like you are doing the same thing I am doing, I'm just trying to do it for an entire laundromat
http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1256657133/0
Oh BTW, you can't wrap around the entire power cord, it has to be just one wire.
Imagine it like this*, one wire has electrons flowing one way, the other has electrons flowing the other. If you wrap it around both, you measure the sum, which is 0.
- Yes I know it's an incorrect way to think about it, but it makes sense that way.
That's exactly what I figured. So that won't work for my purposes, since I can't/don't want to affect the machines in any way.
This option looks promising: The Lucas Eckels Blog ยป Laundrymon, the wireless, noninvasive, Arduino-based, laundry monitor
Basically using the vibration sensor from a couple wii nunchucks to tell when the machines are on.