Postage meter with removable print head

A postage meter includes a printing device (19) which is removable by a user of the postage meter. The printing device may be an ink-jet print cartridge (21) including an integral ink supply. When the ink supply is depleted the ink-jet print cartridge must be replaced to enable further printing to be effected. The printing device has electrical contacts (22) which interface with corresponding electrical connections (20) of the postage meter when the printing device is mounted in the postage meter. In order to prevent unauthorised access to the print device, access to the printing device for replacement of the printing device is provided by means of an aperture (31) in a housing (26) of the postage meter and the aperture is closed by a member (30) which can only be unlocked and opened in response to input of a coded signal to the postage meter.