You king should already blink if you are in check and try to make illegal move.
Do you use a wireless mouse? We have found that wireless mice (mosues ?) don't always hold a consistently depressed click so are prone to accidentally dropping pieces especially when low on battery.
I love chess dot com but have the most frustrating time when I touch a piece and return it, only to discover the system thinks I have actually moved the piece. This is particularly bad then there is a lag.
Is there any method to insure feed back as to my move?
It also frustrates me when sometimes I am in check and do not realise it -can absorb a lot of time -If the system just blinked red on your king or something to make it obvious you are in check, that would resolve that issue very simply