It is a thyristor.
Similar to thermistor but has a slightly different operation
the buzzer will sound for a predetermined time varying on the capacitor value and the LED will stay lit
Swap R4 and SW5 in the second schematic, and remove BZ3 in the first schematic. Then combine them, such that SW2 and SW5 become the same thing, as do SW3 and SW4. But as Mike says, if you will be using an Arduino anyway, then it's much simpler to just connect the switches, buzzer and LED to the Arduino, and do the buzzer and LED control in software.
No it is not remotely similar to a thermistor. And you do not draw it like that. The gate line is a diagonal line leading to the under side of the cathode.http://en.wikipedia.org/wiki/File:SCR_symbol.svg