Yes, in order to act as a Witness it is necessary to keep your wallet open, however this is done in a way that if you use an encrypted wallet your funds will be 100% secure as the wallet will remain encrypted at all times.
Of course, a desktop uses a lot of power, a laptop uses less, but it is not very desirable to leave your laptop on at all times. That’s why a community member developed a wallet for a Raspberry Pi microcomputer that uses only +/- 3 Watt. see G-Dash. There is also a Cloud version developed by the same community member.
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