Lebron23

Hi Gurus I am new in this forum but I start building the ultrasonic radar circuit for my house entrance, but i got stuck with a couple of questions such as: 1. TR1 is a BC547 or BC548 ?? 2. Can I put a buzzer in serial with the colector of TR1, because the relay was not indicated in the circuit i have. Relay details could be find.. Thanks for the help