Pinging tools for checking a device is up

[fluiduk]

Hi All

I have a network of about 10 machines and a few servers, as well as wireless access points and 5 network printers.

Is there a free tool out there that will constantly ping them and alert me if they go down?

As sometimes we just don't notice or staff wont tell me that something isn't working.

Hope this makes sense

Thanks
Aaron