Different studies have shown inconsistent results in time of onset of sleep latency after exposure to RFR from cell phones. Hung and colleagues observed that this could be related to the fact that different modes of cell phone exposure were used. In their study they aimed to determine if sleep latency varied according to the mode used. They used a GSM pulse-modulated cell phone, and randomly exposed 10 healthy young males to either "talk", "listen", "standby", or "sham" mode. The exposure took place for 30 minutes at 13.30 hours, after a night where sleep was restricted to 6 hours. Bipolar EEGs were recorded during and for 90 minutes after exposure.

They found that sleep onset was significantly delayed after "talk" mode exposure, compared to "listen" and "sham" modes. Possible explanations for this observation include: "talk" mode had an SAR of 0.133 mw/KG, while "listen" had  0.015, "standby" had <0.001, and "sham" was zero; there are different ELF components - "talk" mode uses 8 and 217 Hz frequencies, while "listen" has 2, 8, and 217Hz, and "standby" has 1-32 Hz.