The present invention relates to a roaming electronic transaction terminal. It also relates to a secure system for electronic transactions comprising one or more roaming terminals. The terminal (1) has an application package support (2) and a coupler (3) for carrying out the read and write operations on a medium that are required for the electronic transactions in conjunction with the application package. The coupler (3) comprises means for creating a write time window and a read time window on the basis of a secure input signal, all writing and all reading being disabled outside of the corresponding windows. The invention applies notably for the securing of terminals carrying out checks and contractual transactions on supports equipped with processors and memories, it being possible for these supports to be through contactless read and write cards comprising for example transport entitlements, payment means or any other entitlements to be turned to account.