Andy, it doesn't have an audible alert as standard, just a red led. However, because I run radar all the time, the led is constantly illuminated. There is substantial stray energy from the scanner which triggers the Sea-me since it is so close. I have occasionally noticed the led flashing when we've been tied up in harbour and the only active vessels were many miles away.
You can download a pdf Sea-me manual here:
http://www.sea-me.co.uk/pdf/handbook.pdf
