YOU ARE BUYING THE 

SURE-FIRE SERIES TWEETY BIRD WHISTLE.

This sound is available in two series. Regular and "Sure-Fire-Series"... Regular series is  identical to the tweety bird whistle made during the 70's, except we do not use PTP (point to point) assembly anymore. PTP, although it made the device very small, a lot of the transistor arrays were damaged during assembly due to direct soldering to the IC.  Also, costly 1/10w micro resistor were needed in order to allow the device to maintain compactness.  

In 1987 we started using a small PCB as our foundation. It has a "recharge time" needed between key-ups and the longer the wait between key-ups the better it whistles until it reaches full capacity. 

Then there is the "Sure-Fire-Series" which has a small relay keying circuit incorporated on the printed circuit board that insures the whistle to be at maximum at every key-up. Both series has a rapid repeat. There is a slight price difference to defray the added cost of the relay and supporting circuit, plus a little for added labor. 

When activated, either manually through a switch or automatically through the P.T.T. system of the radio, this device generates a mellow whistle which starts at the low end of the audio spectrum and increases in frequency until the whistle goes out of the range of hearing and saturates into a halt.  This version Fires Full Loudness and Sweep at every key-up.