This post explains for the CMOS LSI Chip.
The Part Number is HT2811.
The function of this semiconductor is Ding Dong Door Bell.
Preview images :
The HT2811 is a CMOS LSI chip specially designed for the application of ding-dong door bell. It requir very low nombers of external component and provide low cost, high quality dual tone ding-dong sound. The IC is very suitable for door bell application. […]
1. CMOS metal gate process
2. Low stand-by current : 1μA typically at VDD=3V
3. Good sound quality. (dual tone)
4. envelop adjustable by external RC