Good question

1. **Social Media**: Analyzing tweets, Reddit posts, and other social media mentions can provide insight into public sentiment. Tools and algorithms can be used to track keywords, hashtags, and sentiment around Bitcoin.

2. **News and Media**: Monitoring news articles, headlines, and the tone of media coverage can give an idea of the overall sentiment. Positive news may indicate bullish sentiment, while negative news may suggest bearish sentiment.

3. **Online Forums and Communities**: Forums like Bitcointalk, Reddit's r/Bitcoin, and others can be valuable sources for gauging sentiment. Reading discussions and comments can reveal how users feel about Bitcoin's current and future prospects.

4. **Google Trends**: Tracking the popularity of Bitcoin-related search terms on Google Trends can provide insights into public interest, which often correlates with sentiment.

5. **Market Data**: Analyzing market data, such as price movements, trading volumes, and order book data, can offer insights into trader sentiment. For example, a surge in trading volume may suggest increased interest and bullish sentiment.

6. **Sentiment Analysis Tools**: There are sentiment analysis tools and APIs that can process large amounts of text data and determine sentiment automatically. These tools use machine learning to classify text as positive, negative, or neutral.

7. **Expert Opinions**: Keeping an eye on what well-known figures and experts in the cryptocurrency space are saying about Bitcoin can be indicative of sentiment. Their views can sway the sentiment of the broader community.

But overall social media is the one especially when they are data harvesting the sentiment. Very dangerous