Remotely controlled beeping device

Hello All,
I'm a real Noob to this electronics thing (but I find it fascinating..). Anyway, I want to try to build a device that beeps. The duration and pitch of the beep is fixed, but the frequency should be variable, depending on user input. The whole device should be as small as possible and water proof.
I would prefer to be able to control the beep frequency remotely - perhaps from a mobile phone or from something like a remote controller. The beeping unit should be kept simple as possible.
Any ideas on how I can achieve this?

Thanks,Yossi

Hi Yossi, and welcome.
It would be useful to you to read up a bit on how electricity works, in order to start understanding electronics. Below are some websites that specialise in tutorials and projects for beginners.
You will find many projects for devices that beep in response to all kinds of different inputs.
Look for projects with a "555" or "beeper" in the title.
(By the way, pitch and frequency are the same thing.)

www.learnabout-electronics.org/index.php - Descriptions of components and principles, good diagrams, animations, & fault-finding techniques

http://www.satcure-focus.com/hobby/index.htm - Useful range of ideas tutorials circuits links etc

http://www.allaboutcircuits.com - series of electricity and electronics online textbooks

http://electronics-for-beginners.com/links.php - just what it says on the box

http://www.hobby-hour.com/electronics/ - Teaching from basic principles, resistor code calculators, projects

http://www.radio-electronics.com - useful information and tutorials

http://www.electronics-tutorials.ws/index.html - plus calculators & tools