Recommendations for photocell & altimeter?

Working on a project for a handheld object using ultrasonic sensors that are angled at a 45 degree angle both upwards and downwards these sensors have their own distance range trigger zones which of course onyl trigger if something goes in range or out of their range

The upward sensor works on objects that come into its range.
Whilst the downward sensors works on surfaces that leave the range of the sensor.

As it is a handheld device it will most likely get passed among users of varying heights so I'm looking for a simple altimeter that I can add to my device that will be able to read in the current altitude of the device and then I can use that data to re-calibrate the sensors to the new height reading.

I'm also using a photocell sensor to activate lights on the device when it gets particularly dark. Now would anyone be able to recommend a photocell sensor that would be the next stage up from a micro photocell.

Any recommendations?

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As it is a handheld device it will most likely get passed among users of varying heights so I'm looking for a simple altimeter that I can add to my device that will be able to read in the current altitude of the device

An ultrasonic sensor like the HC-SR04 would be able to do this, if you can guarantee a clear line to the ground, and the sensor pointing exactly down, as pointing at an angle may make the measurement less accurate. Even so, this may not be good enough for you as you have no better than 2 cm resolution, rather coarse when it comes to height differences between people.

I'm also using a photocell sensor to activate lights on the device when it gets particularly dark. Now would anyone be able to recommend a photocell sensor that would be the next stage up from a micro photocell.

A CdS cell would be the simplest, cheapest, but maybe not smallest option. A sensor like the TSL2591 is even smaller and much more accurate, but that's not needed for your application. Do make sure the sensor is placed in such a manner that the users are not covering it with their hands/fingers.

I've already got the SR04's but I'm going to be changing them out for MB7060 XL-MaxSonar-WR1 by MaxBotix

With their main jobs being on obstacle detection & gradient scaling for stairs / kerbs.