Transmission spectra centred on the He I triplet (in the planet rest frame) after removal of the GP model. For each target, different colours refer to the different visits, and the black points show the weighted average over the observations. Vertical dotted black lines indicate the position of the He I triplet. For GJ 3470 b two different transmission spectra are reported, one by considering the two nights not affected by the OH contamination and one by considering only the night responsible for the He I signal. For WASP-69 b, the weighted averaged spectrum has been obtained by excluding the first night (i.e. UT 2019-07-24) as likely affected by stellar contamination.