Humans have a biological predisposition to form attachment to social partners. This attachment, however, is not restricted to humans: non-human and inanimate targets are often involved. People are increasingly engaged with their mobiles but whether their behaviour toward these devices can be regarded as an attachment behaviour has not yet been experimentally tested. Here we hypothesized the existence of mobile attachment. We expected people to seek the proximity of the mobile and give stress response upon separation from it, which manifests both at behavioural and physiological level. We also predicted that separation from the mobile should induce specific separation related emotions, which leads to increased attention to separation-related stimuli. We applied a version of the Strange Situation Test using a mobile phone, with behavioural, physiological, cognitive and self report measures, and the emotional Stroop test. Additionally, we constructed a questionnaire to self assess mobile attachment. Separation from the mobile induced behavioural and physiological stress, proximity seeking behaviour, and an attentional bias to separation-related stimuli for participants with higher mobile attachment. These effects were only observable when no other mobile was present. According to the questionnaire, secure base and safe haven are also relevant aspects of attachment to a mobile. These results support that humans form attachment toward their mobile which is similar to social attachment. This could emerge by cultural recycling of the attachment system's evolutionary structures. (C) 2017 Elsevier Ltd. All rights reserved.