Quantek two button remote control. Coding is by DIP switches and the operating frequency is 433 MHz.

A 418MHz version of this transmitter was produced, but is no longer available. Inside your existing transmitter will be a round sticker. It should say RFM RO2101 OR BCT RTO 433 81. It may be underneath a 'Test OK' sticker, simply remove this to reveal the code.

There can be various letters and numbers either side of the 433, but as long as 433 is somewhere amongst them then this is the 433MHz version. If these numbers do not appear then you have the 418MHz version, and will need to order a replacement controller.