Thermochron

I use these for temperature monitoring but are rather expensive.

I purpose to use a cheap Chinese Nano and temp sensor to do the same.
I would like to be able to sell but may be able to rent/lend .
This is for possibly for assisted living , (UK).
Intent is to devise a cheap system to minimise heating costs for various situations.
Also to make the system easy to use for often elderly owners.

I do not have lots of cash and this is at the moment something of an experiment.

What are the legal problems with this ? i realise that there are some exceptions to CE requirements but not sure of what they are as i no longer have access to the required (expensive) documents for this.

Apologies if this is a double post but earlier one did not stick.