Cut a strip of leather to cover the wire pair, from the switch to almost the ends, leaving about 2″ exposed.
Make a paper pattern first to test the fit. The leather should be approximately 1¼” wide at the top to allow for the switch, and taper down to 1″ at the bottom.
Fold the leather in half lengthwise and sew it together, then slide the 22-gauge wires through using an unbent paper clip.
Strip the wire ends of the snap connector and the siren, leaving ½” exposed. Attach the snap connector to the battery. Place a 1″ length of heat-shrink tubing over the black wire from the siren, then twist this wire to the black wire from the snap connector.
Fold the twisted pair back on itself, slide the heat-shrink tubing over the connection, then use a lighter or heat gun to shrink the tubing around the connection.
Using the same method, connect one of the switch wires to the red wire on the siren, and connect the other switch wire to the red wire on the snap connector. Use 2 short and 2 long pieces of heat-shrink tubing to cover as much of the exposed wire as possible. Test your alarm. It should be ear-piercingly loud.