Electricity

Differences - There are two primary issues. The first is voltage. Electricity in the US is between 110-120 volts. Electricity in Europe is between 220-240 volts. The second is plugs. American plugs have two flat prongs (and possibly a third), while European sockets are made for two round pins. There is a third, less important difference, which I cover below in the Clocks section.

Plug adapters - Plug adapters allow you to physically connect a US plug to a European socket, but they don't alter the electricity at all. If you are bringing a device that is "dual voltage", you will only need a physical adapter for the plug. If your US plug is a two prong plug, the adapter is about 50 cents, if it's a 3-prong plug, expect around $5 for the adapter. You should be able to pick up adapters at any Radio Shack, or you can buy complete adapter sets (for Europe, UK, and other locations) at Brookstone, Sharper Image, or most luggage or travel stores.

Transformer/Voltage converter - If you have a device that can only run on US voltage and you want to bring it along, there is a solution. You can buy transformers that convert both the voltage and the plugs to enable the use of US devices in European sockets. If your device is an electric razor, curling iron, or similar appliance, it should be fine. Be aware though that most heating elements found in a hair dryer or curling iron will run hotter here than at home. It's possible to get converters for more substantial devices, but it's expensive and more complicated, so I'd recommend just leaving them home. Again, small voltage converters can be purchased from any Radio Shack.

How do I know which I need? - If the device has a brick on the plug, you can look there and it will indicate what voltage it can accept. If you see 110-240, then all you need is a plug adapter, but if you see 110-120, then you need the voltage converter. If there's no brick, you can try checking for a tag near the plug or fine print on the plug itself. As a last resort you can look for a small dial/switch on the device that says 110 on one side and 220 on the other. If all that fails, you can try looking for a product description online for your model, or call the manufacturer, but it might not be worth the trouble. Laptops are generally dual voltage (I've *never* seen one that wasn't), as are many curling irons and hair dryers nowadays. Some small appliances (curling irons, shavers, etc.) have a switch that you must change from 110 to 220 before you plug it into the wall.

Clocks/Timers - There is one other subtle difference between electricity in Europe and the US and it has to do with Hertz rate. Electricity in the US is 60 Hertz, but in Europe it's 50 Hertz. Why does this matter? Well, because most simple electronics use the Hertz to count time. Consequently corded alarm clocks and anything with a timer will be off here, even if you use a voltage adapter because the Hertz is not changed. If it's a simple timer, then it will run 20% longer than usual. For instance, my US massage chair has programs that are intended to run for 15 minutes, but here they run for 18 minutes. I don't even notice that difference, but a clock that became 12 minutes behind each hour would be useless. A battery operated clock would be unaffected, of course.