For organisations that are small in size (up to 50 devices) an asset register can be implemented and maintained using an excel spreadsheet or Microsoft Access database.
A template excel spreadsheet for a small organisation can be requested at firstname.lastname@example.org.
Microsoft provide an Access Asset Tracking Template which can be found here.
To help manage more devices you can use Asset Tagging software which allows you to tag assets with an RFID bar code, this is often an easy way of maintaining an asset register.
It is important to keep your asset register up to date. Make sure to add all new devices to the database when purchased and issued to staff, and make sure to remove any assets that are destroyed. Keeping an asset register continuously up to date is a lot easier than trying to build an asset register from an incorrect data set!
For larger organisations we would recommend using a dedicated piece of software. Most IT Service Management (ITSM) software suites include a feature to help manage and track IT assets.