which soudner to use?

i am going to build an IR object detector, like the one shown in the following link:

**broken link removed**

What i want to do is build the circuit and put a sounder on the output. iv had a look on rs components but im not really sure what model to use, as there are quite a few, can anyone help me at all? the cheaper the price the better really :roll:

What kind of sounder depends on what kind of noise you want ot hear..
Just about any electronics supply house will have piezo beepers, they are cheap 3-8 usd and come in pc board mount or surface mount. You could also use a buzzer, but that would require extra circuitry for the higher current draw and emf noise it would create..Same with a horn..
Hope this helps