Using Arduino to switch existing 3v circuit

Hi, I'm a relative newbie when it comes to electronics, so apologies if this is a stupid question. I am trying to modify an existing device so that it can be controlled with an arduino. In it's simplest form, the device has a push button that switches a 3v circuit. I'm thinking that the simplest way to achieve what I'm trying to do is to just mimic the push button. I know I could do this with a relay, but I was just wondering if there's away to do this directly from the arduino? Hope that makes sense.

Thanks Dave

Using a relay gives you one advantage: complete electrical isolation from the device you're controlling. But if you don't need that (i.e. if it's safe to connect the Arduino ground to the 3V device's ground), you can use a transistor, FET or similar device as a switch. If the push button does not carry the full current of the device, but just carries a small signal current, you can use a CMOS switch such as the CD4066 to mimic it.