The “death grip” problem is unfortunately real for the iPhone 4. When skin comes into contact with and bridges the two metal bands in the lower left corner of the iPhone, the displayed signal strength drops. Apple recommends that iPhone 4 owners buy a $30 bumper or other case, which alleviates the problem. Consumer Reports: Consumer Reports says it can’t recommend iPhone 4 to consumers due to the issue. Apple needs to own up to it, and at the very least make the $30 bumpers a free option at the time of purchase.”]
Source: https://www.darkreading.com/database-security/5-ways-to-fix-the-iphone-4-s-antenna-problem