Friend of mine is about to move into temporary rental accommodation which AFAIK doesn't have an alarm, and they'd really prefer to have one.  Since it's a rental it would have to be removable after the rental period which will be at most a few months, so wireless.  There's a pile of these on Aliexpress, e.g. this one which seem OK for the purpose and doesn't cost the earth.  Does anyone have any thoughts on this?  The linked one comes with a decent English manual so seems OK at first glance.