You can use below module to track changes in records by user.

\https://www.odoo.com/apps/modules/8.0/auditlog/

The feature you are looking for is called Auditlog. Several contributors have made different versions of this feature. I would recommend you take a look at https://apps.odoo.com/apps/modules/8.0/auditlog/ by the OCA. It is however not available for version 9, but it is worth trying. Also refer to this https://www.odoo.com/forum/help-1/question/is-audit-log-available-for-odoo-9-version-98123 and see if it helps.

we use odoo9. so i installed https://github.com/Smile-SA/odoo_addons
BUT: ist it possible to track ANY changes in ANY Modules? in the rules it seems that i have to define any field in an extra rule? - that would not be practicable.

Alternatively if there are specific fields you want to track you can use "track_visibility='onchange'".

for example from account.invoice

user_id = fields.Many2one('res.users', string='Salesperson', track_visibility='onchange',        readonly=True, states={'draft': [('readonly', False)]},        default=lambda self: self.env.user)

Someone else may be able to confirm but I believe that the module also has to inherit mail.thread.

_inherit = ['mail.thread']