Rob ter Horst uses a Dreem 2 headband as reference device to test the accuracy of sleep trackers We make the following suggestion for an accurate and affordable reference device: 1. Emotiv Epoc Flex 32 channel EEG device: 1200 USD: 2. Greentek Long-term EEG cap: US $432.81 on Aliexpress: 3. Sleep: An Open-Source Python Software …