Downhole completion with enclosed sensor

A downhole completion system comprising:

• a well tubular metal structure configured to be arranged in a borehole of a well, the well tubular structure having a wall with a through-bore extending radially relative to a longitudinal axis of the well tubular metal structure, and
• a downhole completion device having a housing enclosing a sealed, closed space subject to temperature and/or pressure induced volume changes, the housing being fixedly arranged in the through-bore of the well tubular structure, and
• an electrical component with a sensor arranged in the space inside the housing, the housing being filled with a liquid having a first volume at 1 bar at 20° C.,
• wherein the housing has a first housing section attached inside the though bore of the well tubular structure and a second housing section attached to or formed as part of the first housing section, the second housing section being positioned at a proximal end of the first housing section that is within the through-bore in use, so that the second housing section spans at least part of the through-bore, the first housing section having a first thickness and the second housing section having a second thickness, and the second thickness being smaller than the first thickness so that the second housing section is more flexible than the first housing section, thus protecting the electrical component and sensor from pressure and/or temperature changes downhole while the sensor is configured to measure temperature, pressure or other conditions of the fluid in the well.