We use a mechanical one, a plug with a timer on it. Always worked OK for us. Had it about 20 years now. Digital one would need a battery every now and then.
Also, if you're using energy-saving lights they can sometimes go a bit moody if used with a digital timer, so here's another vote for good old mechanical.
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Would definitely recommend these from Argos, have had them for a couple of years now and use them all the time and they always work well, no problems at all. And you get three in a pack for under 15 quid!
Edit: the link doesn't seem to work so the place is here if you paste into your browser
Edit 2: For some reason the first part of the link above just won't delete no matter what I do (the www.tkqlhce etc part) - can any admin bods help out?
Have used digital ones for years on our reptile tanks. That are more reliable than the manual ones, in which the mechanisms can wear in the cheaper ones. Have never had to replace any backup batteries. The only thing I would say about any type of timer is be careful about setting them to come on and go off at the same time every day if you are using them as a security measure. Nobody manually switches lights on/off at exactly the same time.
------------- It'll work out in the end!!!!
I didn't do it !! Nobody saw me do it !! You can't prove anything !!
i get mine from ikea......use them for slow cooker in caravan....lovely meal ready for when you get back in....
------------- Oct 2013- south lytchett manor dorset
Feb 2014- Lady Heyes
April 2014- Jasmine Park
May 2014 - Jasmine Park Again....
July 2014 - Gwithian
Oct 2014 - Beverley Park